Programs to check given two graphs are isomorphic

#include<iostream>
using namespace std;
#include<stdlib.h>

int V1,E1,V2,E2;
int **graph_1,**graph_2;

struct visited
{
 int data;
 int flag;
};
typedef struct visited visited;

visited *visit1,*visit2; 

int isomorphic()
{
 int i,j,flag;
 if(V1!=V2)
 {
  return 0;
 }
 else
 if(E1!=E2)
 {
  return 0;
 }
 else
 {
        for(i=0;i<V1;i++)
  {
   flag=0;
   for(j=0;j<V2;j++)
   {
         if(visit2[j].flag==0)
      {
          if(visit2[j].data==visit1[i].data)
          {
             visit2[j].flag=visit1[i].flag=1;
             flag=1;
             break;
          }
      }     
   }
   if(!flag)
   break;
  }      
  if(i<V1)
  return 0;
 }
 return 1;
}

int main()
{
    int i,j,v1,v2;
 
 cout<<"\nEnter no. of vertex and edges for graph 1:";
 cin>>V1>>E1;
 
 cout<<"\nEnter no. of vertex and edges for graph 2:";
 cin>>V2>>E2;
 
 graph_1=(int**)malloc(sizeof(int*)*V1);
 for(i=0;i<V1;i++)
 graph_1[i]=(int*)malloc(sizeof(int)*V1);
 
    graph_2=(int**)malloc(sizeof(int*)*V2);
 for(i=0;i<V2;i++)
 graph_2[i]=(int*)malloc(sizeof(int)*V2);
 
 visit1=(visited*)malloc(sizeof(visited)*V1);
 visit2=(visited*)malloc(sizeof(visited)*V2);
 
 for(i=0;i<V1;i++)
  for(j=0;j<V1;j++)
   graph_1[i][j]=0;

 for(i=0;i<V2;i++)
  for(j=0;j<V2;j++)
   graph_2[i][j]=0;
 
 for(i=0;i<V1;i++)
 {
  visit1[i].data=0;
  visit1[i].flag=0;
 }
 for(i=0;i<V2;i++)
 {
  visit2[i].data=0;
  visit2[i].flag=0;
 }
 
 cout<<endl<<"Graph-1 Details :";
 for(i=0;i<E1;i++)
 {
  cout<<"\nEnter vertices for edge "<<i+1<<" :";
  cin>>v1>>v2;
  graph_1[v1-1][v2-1]=1;
  graph_1[v2-1][v1-1]=1;
  visit1[v1-1].data++;
  visit1[v2-1].data++;
 } 
 cout<<endl<<"Graph-2 Details :";
 for(i=0;i<E2;i++)
 {
  cout<<"\nEnter vertices for edge "<<i+1<<" :";
  cin>>v1>>v2;
  graph_2[v1-1][v2-1]=1;
  graph_2[v2-1][v1-1]=1;
  visit2[v1-1].data++;
  visit2[v2-1].data++;
 }
 
  
 if(isomorphic())
 {
  cout<<"\n\nBoth Graphs are Isomorphic"<<endl;
 }
 else
 {
  cout<<"\n\nBoth Graphs are not Isomorphic"<<endl;
 }
 
 return 0;
}