This C++ program, using recursion, displays the number of forward edges in a graph. A forward edge is one in which a node points to one of it’s descendants.

Here is the source code of the C++ program to display the back edges as and when they are encountered. The C++ program is successfully compiled and run on DevCpp, a C++ compiler. The program output is also shown below.

`/*`

`* C++ Program to Implement all Forward Edges in a Graph`

`*/`

`#include<iostream>`

`#include<conio.h>`

using namespace std;

`struct node_info`

`{`

int no;

int lv_time, st_time;

}*q = NULL, *r = NULL;

`struct node`

`{`

node_info *pt;

node *next;

}*top = NULL, *p = NULL, *np = NULL;

`struct node1`

`{`

node1 *link;

node_info *pt1;

}*head = NULL, *m = NULL, *n = NULL, *np1 = NULL;

int c = 0;

void push(node_info *ptr)

`{`

np = new node;

np->pt = ptr;

np->next = NULL;

if (top == NULL)

`{`

top = np;

`}`

`else`

`{`

np->next = top;

top = np;

`}`

`}`

node_info *pop()

`{`

if (top == NULL)

`{`

cout<<"underflow\n";

`}`

`else`

`{`

p = top;

top = top->next;

return(p->pt);

delete(p);

`}`

`}`

void store(node_info *ptr1)

`{`

np1 = new node1;

np1->pt1 = ptr1;

np1->link = NULL;

if (c == 0)

`{`

head = np1;

m = head;

m->link = NULL;

c++;

`}`

`else`

`{`

m = head;

np1->link = m;

head = np1;

`}`

`}`

int search(int j)

`{`

node1 *t = head;

while (t != NULL)

`{`

if ((t->pt1)->no == j)

`{`

break;

`}`

`else`

`{`

t = t->link;

continue;

`}`

`}`

return (t->pt1)->lv_time;

`}`

int present_in_stack(int j)

`{`

int flag = 0;

p = top;

while (p != NULL)

`{`

if ((p->pt)->no == j)

`{`

flag = 1;

return flag;

`}`

p = p->next;

`}`

return flag;

`}`

void topo(int *v, int am[][8], int i)

`{`

q = new node_info;

q->no = i;

q->st_time = c;

push(q);

v[i] = 1;

for (int j = 0; j < 8; j++)

`{`

if (am[i][j] == 0)

continue;

else if (am[i][j] == 1 && v[j] == 1 && !present_in_stack(j))

`{`

if (q->st_time < search(j))

`{`

cout<<"\nForward Edge between "<<i<<" and "<<j<<endl;

`}`

continue;

`}`

else if (am[i][j] == 1 && v[j] == 0)

`{`

c++;

cout<<"\nForward Edge between "<<i<<" and "<<j<<endl;

topo(v,am,j);

`}`

`}`

c++;

q = pop();

q->lv_time = c;

store(q);

return;

`}`

int main()

`{`

int v[8],am[8][8];

for (int i = 0; i < 8; i++)

v[i] = 0;

for (int i = 0; i < 8; i++)

`{`

cout<<"enter the values for adjacency matrix row:"<<i + 1<<endl;

for(int j = 0; j < 8; j++)

`{`

cin>>am[i][j];

`}`

`}`

topo(v,am,0);

getch();

`}`

Output enter the values for adjacency matrix row:1 0 1 0 0 1 0 0 1 enter the values for adjacency matrix row:2 0 0 1 0 0 0 0 0 enter the values for adjacency matrix row:3 0 0 0 1 0 0 0 0 enter the values for adjacency matrix row:4 0 1 0 0 0 0 0 0 enter the values for adjacency matrix row:5 0 0 0 0 0 1 0 0 enter the values for adjacency matrix row:6 0 0 1 0 0 0 1 1 enter the values for adjacency matrix row:7 0 0 0 0 0 0 0 0 enter the values for adjacency matrix row:8 0 0 0 0 0 0 0 0 Forward Edge between 0 and 1 Forward Edge between 1 and 2 Forward Edge between 2 and 3 Forward Edge between 0 and 4 Forward Edge between 4 and 5 Forward Edge between 5 and 6 Forward Edge between 5 and 7 Forward Edge between 0 and 7

**Sanfoundry Global Education & Learning Series – 1000 C++ Programs.**

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