Algorithm to find nth shortest path in a weighted graph

Hello,
I am new to this website. I have recently made a C program, that can graphically simulate the finding of the shortest and 2nd shortest path in a weighted graph. This would be helpful in OSPF routing, where routers can route packets in the 2nd shortest path, if the shortest path has too much traffic. I have formulated the algorithm for finding the nth shortest path in general.To get the source code, visit www.planet-source-code.com.
Do tell me what you think. Thank you.

Might be a good idea to give the exact URL for the source code... there's quite some code on there :D

or post the code here..

the

Code:

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CCC  OOO  DDDD  EEEEE
C  C O  O D  D E
C    O  O D  D EEE
C  C O  O D  D E
 CCC  OOO  DDDD  EEEEE

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tag is there for monospaced stuff..

//**************************************
//
// Name: Graphic Simulation for Shortest
// & 2nd shortest path in a Weighted Graph
// using Dijkstra's Algorithm.
// Description:This program is used as a
// simulation for routing packets between r
// outers. There are 2 subnets, one of whos
// e weights will have to be entered by the
// user(positive only).The user will be ask
// ed for the source and destination nodes,
// for which he has a choice of 0 to 7 ONLY
// .(These are the numbers alotted to the n
// odes). The graphic part will show a gree
// n colored line drawn from the destinatio
// n to the source, that indicates the shor
// test path. This is calculated by Dijkstr
// a's algorithm. If one more packet is des
// ired, a second shortest path is chosen t
// o avoid traffic. This is indicated by th
// e red colored path. Finally, the user en
// ters source and dest for subnet 2(0 to 7
// ONLY).The destination from 1st subnets f
// orwards the packet to the source of 2nd
// subnet, and from there by the shortest p
// ath to the destnation of the 2nd subnet.
// The code uses a second shortest path alg
// orithm, which I have devised.
// By: Abhishek H. Dwivedi
//
// Inputs:User must enter the weights of
// the edges in the first subnet.Then he wi
// ll be asked to enter the source and dest
// ination for the 1st subnet(The choices a
// re from 0 to 7 ONLY as these are the num
// bers assigned to the nodes).For the seco
// nd subnet, the weights are predefined, a
// nd the source and destination entered wi
// ll be again from 0 to 7 only.
//
// Returns:None.Note that the paths are
// drawn from destination to source in all
// cases.
//
//This code is copyrighted and has// limited warranties.Please see http://
// www.Planet-Source-Code.com/vb/scripts/Sh
// owCode.asp?txtCodeId=8733&lngWId=3//for details.//**************************************
//

#include<stdio.h>
#include<conio.h>
#include<graphics.h>
#include<dos.h>
float sum=0,w=0,s,wn,v[8],td=0,e,i,j,n,w1[8],j1[8],arr[8],arr1[8],e1,count,d2,y1;
float var,a[8][8],d[8],p[8],n1,c,c1,w2;
void main()


{
int gd=DETECT,gm,count1=0;
clrscr();
void draw(float,float);
void dijkstra(float s,float e,float v1[8],float d1[8],float p1[8],float a1[8][8],float n);
void ssp();
void path();
void initial();
printf("There are 8 routers in each subnet\n");
n=8;
for(i=0;i<n;i++)


{
for(j=0;j<n;j++)


{
a[i][j]=32767;
}}
printf("Enter the weight between 0 & 1 : ");
scanf("%f",&a[0][1]);
a[1][0]=a[0][1];
printf("Enter the weight between 0 & 3 : ");
scanf("%f",&a[0][3]);
a[3][0]=a[0][3];
printf("Enter the weight between 1 & 5 : ");
scanf("%f",&a[1][5]);
a[5][1]=a[1][5];
printf("Enter the weight between 1 & 2 : ");
scanf("%f",&a[1][2]);
a[2][1]=a[1][2];
printf("Enter the weight between 2 & 4 : ");
scanf("%f",&a[2][4]);
a[4][2]=a[2][4];
printf("Enter the weight between 2 & 3 : ");
scanf("%f",&a[2][3]);
a[3][2]=a[2][3];
printf("Enter the weight between 3 & 7 : ");
scanf("%f",&a[3][7]);
a[7][3]=a[3][7];
printf("Enter the weight between 4 & 5 : ");
scanf("%f",&a[4][5]);
a[5][4]=a[4][5];
printf("Enter the weight between 4 & 7 : ");
scanf("%f",&a[4][7]);
a[7][4]=a[4][7];
printf("Enter the weight between 5 & 6 : ");
scanf("%f",&a[5][6]);
a[6][5]=a[5][6];
printf("Enter the weight between 6 & 7 : ");
scanf("%f",&a[6][7]);
a[7][6]=a[6][7];
printf("Enter source and destination node from network 1 ");
scanf("%f %f",&s,&e);
clrscr();
initgraph(&gd,&gm,"c:\\tc\\bgi");
setcolor(WHITE);
fillellipse(20,100,7,7);fillellipse(85,50,7,7);
fillellipse(150,100,7,7);fillellipse(85,150,7,7);
fillellipse(320,100,7,7);fillellipse(385,50,7,7);
fillellipse(450,100,7,7);fillellipse(385,150,7,7);
w1[0]=20;w1[1]=85;w1[2]=150;w1[3]=85;w1[4]=320;
w1[5]=385;w1[6]=450;w1[7]=385;
j1[0]=100;j1[1]=50;j1[2]=100;j1[3]=150;j1[4]=100;j1[5]=50;
j1[6]=100;j1[7]=150;
initial();
setcolor(GREEN);
for(i=0;i<n;i++)


{
v[i]=32767;
d[i]=32767;
p[i]=0;
}
w=s;
d[s]=0;
v[s]=s;
td=0;
dijkstra(s,e,v,d,p,a,n);
path();
c=w1[e];
c1=j1[e];
printf("One more packet ?(Type 1 if yes) ");
scanf("%f",&count);
path();
if(count==1)


{
ssp();
count1=1;
}
path();
w=e;
setcolor(GREEN);
count=0;
printf("Enter source and destination node from network 2 ");
scanf("%f %f",&s,&e);
a[0][1]=2;
a[0][3]=6;
a[1][2]=2;
a[1][5]=7;
a[2][3]=1;
a[2][4]=2;
a[4][5]=3;
a[5][6]=3;
a[4][7]=2;
a[6][7]=2;
a[3][7]=4;
a[1][0]=2;
a[3][0]=6;
a[2][1]=2;
a[5][1]=7;
a[3][2]=1;
a[4][2]=2;
a[5][4]=3;
a[6][5]=3;
a[7][4]=2;
a[7][6]=2;
a[7][3]=4;
setcolor(WHITE);
fillellipse(20,400,7,7);fillellipse(85,350,7,7);
fillellipse(150,400,7,7);fillellipse(85,450,7,7);
fillellipse(320,400,7,7);fillellipse(385,350,7,7);
fillellipse(450,400,7,7);fillellipse(385,450,7,7);
w1[0]=20;w1[1]=85;w1[2]=150;w1[3]=85;w1[4]=320;
w1[5]=385;w1[6]=450;w1[7]=385;
j1[0]=400;j1[1]=350;j1[2]=400;j1[3]=450;j1[4]=400;j1[5]=350;
j1[6]=400;j1[7]=450;
initial();
setcolor(GREEN);
for(i=0;i<n;i++)


{
v[i]=32767;
d[i]=32767;
p[i]=0;
}
w=s;
d[s]=0;
v[s]=s;
td=0;
line(c,c1,w1[s],j1[s]);
delay(2000);
dijkstra(s,e,v,d,p,a,n);
path();
count=1;
if(count1==1)
ssp();
path();
getch();
}
void dijkstra(float s,float e,float v1[8],float d1[8],float p1[8],float a1[8][8],float n)


{
while((p1[e])==0)


{
for(i=0;i<n;i++)


{
if((a1[w][i]+td)<d1[i]&&i!=w&&a1[w][i]!=32767)


{
d1[i]=a1[w][i]+td;
d2=d1[i];
v1[i]=w;
}}
sum=32767;
for(i=0;i<n;i++)


{
if(d1[i]<sum&&i!=s&&p1[i]!=1)


{
sum=d1[i];
wn=i;
}}
p1[wn]=1;
td=d1[wn];
w=wn;
}
}
void draw(float w,float v1)


{
float s,x,y;
s=(j1[v1]-j1[w])/(w1[v1]-w1[w]);
if(s<0)
s=s*-1;
x=w1[w];
y=j1[w];
moveto(x,y);
if(x==w1[v1])


{
while(y!=j1[v1])


{
if(y>j1[v1])


{
line(x,y,x,y-1);
delay(10);
y=y-1;
}
else


{
line(x,y,x,y+1);
delay(10);
y=y+1;
}}}
if(y==j1[v1])


{
while(x!=w1[v1])


{
if(x>w1[v1])


{
line(x,y,x-1,y);
delay(10);
x=x-1;
}
else


{
line(x,y,x+1,y);
delay(10);
x=x+1;
}}}
if(x<w1[v1]&&y<j1[v1])


{
while(x!=w1[v1])


{
line(x,y,x+1,y+s);
delay(10);
x=x+1;
y=y+s;
}}
if(x>w1[v1]&&y>j1[v1])


{
while(x!=w1[v1])


{
line(x,y,x-1,y-s);
delay(10);
x=x-1;
y=y-s;
i=i+1;
}}
if(x>w1[v1]&&y<j1[v1])


{
while(x!=w1[v1])


{
line(x,y,x-1,y+s);
delay(10);
x=x-1;
y=y+s;
i=i+1;
}}
if(x<w1[v1]&&y>j1[v1])


{
while(x!=w1[v1])


{
line(x,y,x+1,y-s);
delay(10);
x=x+1;
y=y-s;

dude, try the [ code ] tag, please !!

There's an edit button on top of your post..

Hello again,
I am pasting the source code here as requested by Jinx.
//**************************************
//
// Name: Graphic Simulation for Shortest
// & 2nd shortest path in a Weighted Graph
// using Dijkstra's Algorithm.
// Description:This program is used as a
// simulation for routing packets between r
// outers. There are 2 subnets, one of whos
// e weights will have to be entered by the
// user(positive only).The user will be ask
// ed for the source and destination nodes,
// for which he has a choice of 0 to 7 ONLY
// .(These are the numbers alotted to the n
// odes). The graphic part will show a gree
// n colored line drawn from the destinatio
// n to the source, that indicates the shor
// test path. This is calculated by Dijkstr
// a's algorithm. If one more packet is des
// ired, a second shortest path is chosen t
// o avoid traffic. This is indicated by th
// e red colored path. Finally, the user en
// ters source and dest for subnet 2(0 to 7
// ONLY).The destination from 1st subnets f
// orwards the packet to the source of 2nd
// subnet, and from there by the shortest p
// ath to the destnation of the 2nd subnet.
// The code uses a second shortest path alg
// orithm, which I have devised.
// By: Abhishek H. Dwivedi
//
// Inputs:User must enter the weights of
// the edges in the first subnet.Then he wi
// ll be asked to enter the source and dest
// ination for the 1st subnet(The choices a
// re from 0 to 7 ONLY as these are the num
// bers assigned to the nodes).For the seco
// nd subnet, the weights are predefined, a
// nd the source and destination entered wi
// ll be again from 0 to 7 only.
//
// Returns:None.Note that the paths are
// drawn from destination to source in all
// cases.
//
//This code is copyrighted and has// limited warranties.Please see http://
// www.Planet-Source-Code.com/vb/scripts/Sh
// owCode.asp?txtCodeId=8733&lngWId=3//for details.//**************************************
//

#include<stdio.h>
#include<conio.h>
#include<graphics.h>
#include<dos.h>
float sum=0,w=0,s,wn,v[8],td=0,e,i,j,n,w1[8],j1[8],arr[8],arr1[8],e1,count,d2,y1;
float var,a[8][8],d[8],p[8],n1,c,c1,w2;
void main()


{
int gd=DETECT,gm,count1=0;
clrscr();
void draw(float,float);
void dijkstra(float s,float e,float v1[8],float d1[8],float p1[8],float a1[8][8],float n);
void ssp();
void path();
void initial();
printf("There are 8 routers in each subnet\n");
n=8;
for(i=0;i<n;i++)


{
for(j=0;j<n;j++)


{
a[i][j]=32767;
}}
printf("Enter the weight between 0 & 1 : ");
scanf("%f",&a[0][1]);
a[1][0]=a[0][1];
printf("Enter the weight between 0 & 3 : ");
scanf("%f",&a[0][3]);
a[3][0]=a[0][3];
printf("Enter the weight between 1 & 5 : ");
scanf("%f",&a[1][5]);
a[5][1]=a[1][5];
printf("Enter the weight between 1 & 2 : ");
scanf("%f",&a[1][2]);
a[2][1]=a[1][2];
printf("Enter the weight between 2 & 4 : ");
scanf("%f",&a[2][4]);
a[4][2]=a[2][4];
printf("Enter the weight between 2 & 3 : ");
scanf("%f",&a[2][3]);
a[3][2]=a[2][3];
printf("Enter the weight between 3 & 7 : ");
scanf("%f",&a[3][7]);
a[7][3]=a[3][7];
printf("Enter the weight between 4 & 5 : ");
scanf("%f",&a[4][5]);
a[5][4]=a[4][5];
printf("Enter the weight between 4 & 7 : ");
scanf("%f",&a[4][7]);
a[7][4]=a[4][7];
printf("Enter the weight between 5 & 6 : ");
scanf("%f",&a[5][6]);
a[6][5]=a[5][6];
printf("Enter the weight between 6 & 7 : ");
scanf("%f",&a[6][7]);
a[7][6]=a[6][7];
printf("Enter source and destination node from network 1 ");
scanf("%f %f",&s,&e);
clrscr();
initgraph(&gd,&gm,"c:\\tc\\bgi");
setcolor(WHITE);
fillellipse(20,100,7,7);fillellipse(85,50,7,7);
fillellipse(150,100,7,7);fillellipse(85,150,7,7);
fillellipse(320,100,7,7);fillellipse(385,50,7,7);
fillellipse(450,100,7,7);fillellipse(385,150,7,7);
w1[0]=20;w1[1]=85;w1[2]=150;w1[3]=85;w1[4]=320;
w1[5]=385;w1[6]=450;w1[7]=385;
j1[0]=100;j1[1]=50;j1[2]=100;j1[3]=150;j1[4]=100;j1[5]=50;
j1[6]=100;j1[7]=150;
initial();
setcolor(GREEN);
for(i=0;i<n;i++)


{
v[i]=32767;
d[i]=32767;
p[i]=0;
}
w=s;
d[s]=0;
v[s]=s;
td=0;
dijkstra(s,e,v,d,p,a,n);
path();
c=w1[e];
c1=j1[e];
printf("One more packet ?(Type 1 if yes) ");
scanf("%f",&count);
path();
if(count==1)


{
ssp();
count1=1;
}
path();
w=e;
setcolor(GREEN);
count=0;
printf("Enter source and destination node from network 2 ");
scanf("%f %f",&s,&e);
a[0][1]=2;
a[0][3]=6;
a[1][2]=2;
a[1][5]=7;
a[2][3]=1;
a[2][4]=2;
a[4][5]=3;
a[5][6]=3;
a[4][7]=2;
a[6][7]=2;
a[3][7]=4;
a[1][0]=2;
a[3][0]=6;
a[2][1]=2;
a[5][1]=7;
a[3][2]=1;
a[4][2]=2;
a[5][4]=3;
a[6][5]=3;
a[7][4]=2;
a[7][6]=2;
a[7][3]=4;
setcolor(WHITE);
fillellipse(20,400,7,7);fillellipse(85,350,7,7);
fillellipse(150,400,7,7);fillellipse(85,450,7,7);
fillellipse(320,400,7,7);fillellipse(385,350,7,7);
fillellipse(450,400,7,7);fillellipse(385,450,7,7);
w1[0]=20;w1[1]=85;w1[2]=150;w1[3]=85;w1[4]=320;
w1[5]=385;w1[6]=450;w1[7]=385;
j1[0]=400;j1[1]=350;j1[2]=400;j1[3]=450;j1[4]=400;j1[5]=350;
j1[6]=400;j1[7]=450;
initial();
setcolor(GREEN);
for(i=0;i<n;i++)


{
v[i]=32767;
d[i]=32767;
p[i]=0;
}
w=s;
d[s]=0;
v[s]=s;
td=0;
line(c,c1,w1[s],j1[s]);
delay(2000);
dijkstra(s,e,v,d,p,a,n);
path();
count=1;
if(count1==1)
ssp();
path();
getch();
}
void dijkstra(float s,float e,float v1[8],float d1[8],float p1[8],float a1[8][8],float n)


{
while((p1[e])==0)


{
for(i=0;i<n;i++)


{
if((a1[w][i]+td)<d1[i]&&i!=w&&a1[w][i]!=32767)


{
d1[i]=a1[w][i]+td;
d2=d1[i];
v1[i]=w;
}}
sum=32767;
for(i=0;i<n;i++)


{
if(d1[i]<sum&&i!=s&&p1[i]!=1)


{
sum=d1[i];
wn=i;
}}
p1[wn]=1;
td=d1[wn];
w=wn;
}
}
void draw(float w,float v1)


{
float s,x,y;
s=(j1[v1]-j1[w])/(w1[v1]-w1[w]);
if(s<0)
s=s*-1;
x=w1[w];
y=j1[w];
moveto(x,y);
if(x==w1[v1])


{
while(y!=j1[v1])


{
if(y>j1[v1])


{
line(x,y,x,y-1);
delay(10);
y=y-1;
}
else


{
line(x,y,x,y+1);
delay(10);
y=y+1;
}}}
if(y==j1[v1])


{
while(x!=w1[v1])


{
if(x>w1[v1])


{
line(x,y,x-1,y);
delay(10);
x=x-1;
}
else


{
line(x,y,x+1,y);
delay(10);
x=x+1;
}}}
if(x<w1[v1]&&y<j1[v1])


{
while(x!=w1[v1])


{
line(x,y,x+1,y+s);
delay(10);
x=x+1;
y=y+s;
}}
if(x>w1[v1]&&y>j1[v1])


{
while(x!=w1[v1])


{
line(x,y,x-1,y-s);
delay(10);
x=x-1;
y=y-s;
i=i+1;
}}
if(x>w1[v1]&&y<j1[v1])


{
while(x!=w1[v1])


{
line(x,y,x-1,y+s);
delay(10);
x=x-1;
y=y+s;
i=i+1;
}}
if(x<w1[v1]&&y>j1[v1])


{
while(x!=w1[v1])


{
line(x,y,x+1,y-s);
delay(10);
x=x+1;
y=y-s;
i=i+1;
}
}}
void ssp()


{
d2=y1=32767;
setcolor(RED);
e1=e;
for(i=0;i<n;i++)


{
arr1[i]=v[i];
arr[i]=v[i];
}
while(e1!=s)


{
var=a[e1][arr1[e1]]=a[arr1[e1]][e1];
a[e1][arr1[e1]]=a[arr1[e1]][e1]=32767;
for(i=0;i<n;i++)


{
v[i]=32767;
d[i]=32767;
p[i]=0;
}
w=s;d[s]=0;
v[s]=s;
td=0;
dijkstra(s,e,v,d,p,a,n);
if(td<y1)


{
y1=td;
for(i=0;i<n;i++)
arr[i]=v[i];
}
a[e1][arr1[e1]]=a[arr1[e1]][e1]=var;
e1=arr1[e1];
}}
void path()


{
while(w!=s)


{
if(count==0)


{
draw(w,v[w]);
w=v[w];
}
else


{
draw(w,arr[w]);
w=arr[w];
}}}
void initial()


{
line(w1[0],j1[0],w1[1],j1[1]);
line(w1[0],j1[0],w1[3],j1[3]);
line(w1[1],j1[1],w1[5],j1[5]);
line(w1[1],j1[1],w1[2],j1[2]);
line(w1[2],j1[2],w1[4],j1[4]);
line(w1[2],j1[2],w1[3],j1[3]);
line(w1[3],j1[3],w1[7],j1[7]);
line(w1[4],j1[4],w1[5],j1[5]);
line(w1[4],j1[4],w1[7],j1[7]);
line(w1[5],j1[5],w1[6],j1[6]);
line(w1[6],j1[6],w1[7],j1[7]);
}

Hi,

Here you go .................. the_JinX ment to put the Code in the [ Code ] tag ............and not to post the Code again :p .................it's very hard to read the Code like that .

Code:

---

Terms of Agreement: 
By using this code, you agree to the following terms... 
1) You may use this code in your own programs (and may compile it into a program and distribute it in compiled format for languages that allow it) freely and with no charge. 
2) You MAY NOT redistribute this code (for example to a web site) without written permission from the original author. Failure to do so is a violation of copyright laws. 
3) You may link to this code from another website, but ONLY if it is not wrapped in a frame.
4) You will abide by any additional copyright restrictions which the author may have placed in the code or code's description.


//**************************************
//   
// Name: Graphic Simulation for Shortest
//    & 2nd shortest path in a Weighted Graph
//    using Dijkstra's Algorithm.
// Description:This program is used as a
//    simulation for routing packets between r
//    outers. There are 2 subnets, one of whos
//    e weights will have to be entered by the
//    user(positive only).The user will be ask
//    ed for the source and destination nodes,
//    for which he has a choice of 0 to 7 ONLY
//    .(These are the numbers alotted to the n
//    odes). The graphic part will show a gree
//    n colored line drawn from the destinatio
//    n to the source, that indicates the shor
//    test path. This is calculated by Dijkstr
//    a's algorithm. If one more packet is des
//    ired, a second shortest path is chosen t
//    o avoid traffic. This is indicated by th
//    e red colored path. Finally, the user en
//    ters source and dest for subnet 2(0 to 7
//    ONLY).The destination from 1st subnets f
//    orwards the packet to the source of 2nd
//    subnet, and from there by the shortest p
//    ath to the destnation of the 2nd subnet.
//    The code uses a second shortest path alg
//    orithm, which I have devised.
// By: Abhishek H. Dwivedi
//
// Inputs:User must enter the weights of
//    the edges in the first subnet.Then he wi
//    ll be asked to enter the source and dest
//    ination for the 1st subnet(The choices a
//    re from 0 to 7 ONLY as these are the num
//    bers assigned to the nodes).For the seco
//    nd subnet, the weights are predefined, a
//    nd the source and destination entered wi
//    ll be again from 0 to 7 only.
//
// Returns:None.Note that the paths are
//    drawn from destination to source in all
//    cases.
//
//This code is copyrighted and has// limited warranties.Please see http://
//    www.Planet-Source-Code.com/vb/scripts/Sh
//    owCode.asp?txtCodeId=8733&lngWId=3//for details.//**************************************
//   

#include<stdio.h>
#include<conio.h>
#include<graphics.h>
#include<dos.h>
float sum=0,w=0,s,wn,v[8],td=0,e,i,j,n,w1[8],j1[8],arr[8],arr1[8],e1,count,d2,y1;
float var,a[8][8],d[8],p[8],n1,c,c1,w2;
void main()


    {
    int gd=DETECT,gm,count1=0;
    clrscr();
    void draw(float,float);
    void dijkstra(float s,float e,float v1[8],float d1[8],float p1[8],float a1[8][8],float n);
    void ssp();
    void path();
    void initial();
    printf("There are 8 routers in each subnet\n");
    n=8;
    for(i=0;i<n;i++)


        {
        for(j=0;j<n;j++)


            {
            a[i][j]=32767;
        }}

        printf("Enter the weight between 0 & 1 : ");
        scanf("%f",&a[0][1]);
        a[1][0]=a[0][1];
        printf("Enter the weight between 0 & 3 : ");
        scanf("%f",&a[0][3]);
        a[3][0]=a[0][3];
        printf("Enter the weight between 1 & 5 : ");
        scanf("%f",&a[1][5]);
        a[5][1]=a[1][5];
        printf("Enter the weight between 1 & 2 : ");
        scanf("%f",&a[1][2]);
        a[2][1]=a[1][2];
        printf("Enter the weight between 2 & 4 : ");
        scanf("%f",&a[2][4]);
        a[4][2]=a[2][4];
        printf("Enter the weight between 2 & 3 : ");
        scanf("%f",&a[2][3]);
        a[3][2]=a[2][3];
        printf("Enter the weight between 3 & 7 : ");
        scanf("%f",&a[3][7]);
        a[7][3]=a[3][7];
        printf("Enter the weight between 4 & 5 : ");
        scanf("%f",&a[4][5]);
        a[5][4]=a[4][5];
        printf("Enter the weight between 4 & 7 : ");
        scanf("%f",&a[4][7]);
        a[7][4]=a[4][7];
        printf("Enter the weight between 5 & 6 : ");
        scanf("%f",&a[5][6]);
        a[6][5]=a[5][6];
        printf("Enter the weight between 6 & 7 : ");
        scanf("%f",&a[6][7]);
        a[7][6]=a[6][7];
        printf("Enter source and destination node from network 1 ");
        scanf("%f %f",&s,&e);
        clrscr();
        initgraph(&gd,&gm,"c:\\tc\\bgi");
        setcolor(WHITE);
        fillellipse(20,100,7,7);fillellipse(85,50,7,7);
        fillellipse(150,100,7,7);fillellipse(85,150,7,7);
        fillellipse(320,100,7,7);fillellipse(385,50,7,7);
        fillellipse(450,100,7,7);fillellipse(385,150,7,7);
        w1[0]=20;w1[1]=85;w1[2]=150;w1[3]=85;w1[4]=320;
        w1[5]=385;w1[6]=450;w1[7]=385;
        j1[0]=100;j1[1]=50;j1[2]=100;j1[3]=150;j1[4]=100;j1[5]=50;
        j1[6]=100;j1[7]=150;
        initial();
        setcolor(GREEN);
        for(i=0;i<n;i++)


            {
            v[i]=32767;
            d[i]=32767;
            p[i]=0;
        }

        w=s;
        d[s]=0;
        v[s]=s;
        td=0;
        dijkstra(s,e,v,d,p,a,n);
        path();
        c=w1[e];
        c1=j1[e];
        printf("One more packet ?(Type 1 if yes) ");
        scanf("%f",&count);
        path();
        if(count==1)


            {
            ssp();
            count1=1;
        }

        path();
        w=e;
        setcolor(GREEN);
        count=0;
        printf("Enter source and destination node from network 2 ");
        scanf("%f %f",&s,&e);
        a[0][1]=2;
        a[0][3]=6;
        a[1][2]=2;
        a[1][5]=7;
        a[2][3]=1;
        a[2][4]=2;
        a[4][5]=3;
        a[5][6]=3;
        a[4][7]=2;
        a[6][7]=2;
        a[3][7]=4;
        a[1][0]=2;
        a[3][0]=6;
        a[2][1]=2;
        a[5][1]=7;
        a[3][2]=1;
        a[4][2]=2;
        a[5][4]=3;
        a[6][5]=3;
        a[7][4]=2;
        a[7][6]=2;
        a[7][3]=4;
        setcolor(WHITE);
        fillellipse(20,400,7,7);fillellipse(85,350,7,7);
        fillellipse(150,400,7,7);fillellipse(85,450,7,7);
        fillellipse(320,400,7,7);fillellipse(385,350,7,7);
        fillellipse(450,400,7,7);fillellipse(385,450,7,7);
        w1[0]=20;w1[1]=85;w1[2]=150;w1[3]=85;w1[4]=320;
        w1[5]=385;w1[6]=450;w1[7]=385;
        j1[0]=400;j1[1]=350;j1[2]=400;j1[3]=450;j1[4]=400;j1[5]=350;
        j1[6]=400;j1[7]=450;
        initial();
        setcolor(GREEN);
        for(i=0;i<n;i++)


            {
            v[i]=32767;
            d[i]=32767;
            p[i]=0;
        }

        w=s;
        d[s]=0;
        v[s]=s;
        td=0;
        line(c,c1,w1[s],j1[s]);
        delay(2000);
        dijkstra(s,e,v,d,p,a,n);
        path();
        count=1;
        if(count1==1)
        ssp();
        path();
        getch();
    }

    void dijkstra(float s,float e,float v1[8],float d1[8],float p1[8],float a1[8][8],float n)


        {
        while((p1[e])==0)


            {
            for(i=0;i<n;i++)


                {
                if((a1[w][i]+td)<d1[i]&&i!=w&&a1[w][i]!=32767)


                    {
                    d1[i]=a1[w][i]+td;
                    d2=d1[i];
                    v1[i]=w;
                }}

                sum=32767;
                for(i=0;i<n;i++)


                    {
                    if(d1[i]<sum&&i!=s&&p1[i]!=1)


                        {
                        sum=d1[i];
                        wn=i;
                    }}

                    p1[wn]=1;
                    td=d1[wn];
                    w=wn;
                }

            }

            void draw(float w,float v1)


                {
                float s,x,y;
                s=(j1[v1]-j1[w])/(w1[v1]-w1[w]);
                if(s<0)
                s=s*-1;
                x=w1[w];
                y=j1[w];
                moveto(x,y);
                if(x==w1[v1])


                    {
                    while(y!=j1[v1])


                        {
                        if(y>j1[v1])


                            {
                            line(x,y,x,y-1);
                            delay(10);
                            y=y-1;
                        }

                        else


                            {
                            line(x,y,x,y+1);
                            delay(10);
                            y=y+1;
                        }}}

                        if(y==j1[v1])


                            {
                            while(x!=w1[v1])


                                {
                                if(x>w1[v1])


                                    {
                                    line(x,y,x-1,y);
                                    delay(10);
                                    x=x-1;
                                }

                                else


                                    {
                                    line(x,y,x+1,y);
                                    delay(10);
                                    x=x+1;
                                }}}

                                if(x<w1[v1]&&y<j1[v1])


                                    {
                                    while(x!=w1[v1])


                                        {
                                        line(x,y,x+1,y+s);
                                        delay(10);
                                        x=x+1;
                                        y=y+s;
                                    }}

                                    if(x>w1[v1]&&y>j1[v1])


                                        {
                                        while(x!=w1[v1])


                                            {
                                            line(x,y,x-1,y-s);
                                            delay(10);
                                            x=x-1;
                                            y=y-s;
                                            i=i+1;
                                        }}

                                        if(x>w1[v1]&&y<j1[v1])


                                            {
                                            while(x!=w1[v1])


                                                {
                                                line(x,y,x-1,y+s);
                                                delay(10);
                                                x=x-1;
                                                y=y+s;
                                                i=i+1;
                                            }}

                                            if(x<w1[v1]&&y>j1[v1])


                                                {
                                                while(x!=w1[v1])


                                                    {
                                                    line(x,y,x+1,y-s);
                                                    delay(10);
                                                    x=x+1;
                                                    y=y-s;
                                                    i=i+1;
                                                }

                                            }}

                                            void ssp()


                                                {
                                                d2=y1=32767;
                                                setcolor(RED);
                                                e1=e;
                                                for(i=0;i<n;i++)


                                                    {
                                                    arr1[i]=v[i];
                                                    arr[i]=v[i];
                                                }

                                                while(e1!=s)


                                                    {
                                                    var=a[e1][arr1[e1]]=a[arr1[e1]][e1];
                                                    a[e1][arr1[e1]]=a[arr1[e1]][e1]=32767;
                                                    for(i=0;i<n;i++)


                                                        {
                                                        v[i]=32767;
                                                        d[i]=32767;
                                                        p[i]=0;
                                                    }

                                                    w=s;d[s]=0;
                                                    v[s]=s;
                                                    td=0;
                                                    dijkstra(s,e,v,d,p,a,n);
                                                    if(td<y1)


                                                        {
                                                        y1=td;
                                                        for(i=0;i<n;i++)
                                                        arr[i]=v[i];
                                                    }

                                                    a[e1][arr1[e1]]=a[arr1[e1]][e1]=var;
                                                    e1=arr1[e1];
                                                }}

                                                void path()


                                                    {
                                                    while(w!=s)


                                                        {
                                                        if(count==0)


                                                            {
                                                            draw(w,v[w]);
                                                            w=v[w];
                                                        }

                                                        else


                                                            {
                                                            draw(w,arr[w]);
                                                            w=arr[w];
                                                        }}}

                                                        void initial()


                                                            {
                                                            line(w1[0],j1[0],w1[1],j1[1]);
                                                            line(w1[0],j1[0],w1[3],j1[3]);
                                                            line(w1[1],j1[1],w1[5],j1[5]);
                                                            line(w1[1],j1[1],w1[2],j1[2]);
                                                            line(w1[2],j1[2],w1[4],j1[4]);
                                                            line(w1[2],j1[2],w1[3],j1[3]);
                                                            line(w1[3],j1[3],w1[7],j1[7]);
                                                            line(w1[4],j1[4],w1[5],j1[5]);
                                                            line(w1[4],j1[4],w1[7],j1[7]);
                                                            line(w1[5],j1[5],w1[6],j1[6]);
                                                            line(w1[6],j1[6],w1[7],j1[7]);
                                                        }

---

Source

Makes it more readable.............. :)

--Good Luck--

Hello,
Thank you sword_fish,and Jinx for your suggestions.Here is the algorithm to find the 2nd shortest path.Once you find the shortest path by Dijkstra's algorithm (or Bellman-Ford also),
make the last edge of the path equal to infinity, thus cutting it off from the graph.Then run the dijkstra's algorithm again.Restore that edge,and make the second edge=infinity,and continue so on for all edges.The shortest path amongst the collection of all those, will be the 2nd shortest path in the graph.