deletion of nodes and edges in a graph

Program for addition and deletion of nodes and edges in a graph   using adjacency matrix */
#include<stdio.h>
#define max 20
int adj[max][max];
int n;
main()
{
int choice;
int node,origin,destin;
create_graph();
while(1)
{
printf("1.Insert a node\n");
printf("2.Insert an edge\n");
printf("3.Delete a node\n");
printf("4.Delete an edge\n");
printf("5.Dispaly\n");
printf("6.Exit\n");
printf("Enter your choice : ");
scanf("%d",&choice);
switch(choice)
{
case 1:
insert_node();
break;
case 2:
printf("Enter an edge to be inserted : ");
fflush(stdin);
scanf("%d %d",&origin,&destin);
insert_edge(origin,destin);
break;
case 3:
printf("Enter a node to be deleted : ");
fflush(stdin);
scanf("%d",&node);
delete_node(node);
break;
case 4:
printf("Enter an edge to be deleted : ");
fflush(stdin);
scanf("%d %d",&origin,&destin);
del_edge(origin,destin);
break;
case 5:
display();
break;
case 6:
exit();
default: printf("Wrong choice\n");
break;
}/*End of switch*/
}/*End of while*/
}/*End of main()
*/
create_graph()
{
int i,max_edges,origin,destin;
printf("Enter number of nodes : ");
scanf("%d",&n);
max_edges=n*(n-1);
/* Taking directed graph */
for(i=1;i<=max_edges;i++)
{
printf("Enter edge %d( 0 0 ) to quit : ",i);
scanf("%d %d",&origin,&destin);
if((origin==0) && (destin==0))
break;
if( origin > n || destin > n || origin<=0 || destin<=0)
{
printf("Invalid edge!\n");
i--;
}
else
adj[origin][destin]=1;
}/*End of for*/
}/*End of create_graph()*/
display()
{
int i,j;
for(i=1;i<=n;i++)
{
for(j=1;j<=n;j++)
printf("%4d",adj[i][j]);
printf("\n");
}
}/*End of display()*/
insert_node()
{
int i;
n++;
    /*Increase number of nodes in the graph*/
printf("The inserted node is %d \n",n);
for(i=1;i<=n;i++)
{
adj[i][n]=0;
adj[n][i]=0;
}
}/*End of insert_node()*/
delete_node(char u)
{
int i,j;
if(n==0)
{
printf("Graph is empty\n");
return;
}
if( u>n )
{
printf("This node is not present in the graph\n");
return;
}
for(i=u;i<=n-1;i++)
   for(j=1;j<=n;j++)
   {
adj[j][i]=adj[j][i+1];
  /* Shift columns left */
adj[i][j]=adj[i+1][j];
  /* Shift rows up */
   }
n--;
/*Decrease the number of nodes in the graph */
}/*End of delete_node*/
insert_edge(char u,char v)
{
if(u > n)
{
printf("Source node does not exist\n");
return;
}
if(v > n)
{
printf("Destination node does not exist\n");
return;
}
adj[u][v]=1;
}/*End of insert_edge()*/
del_edge(char u,char v)
{
     if(u>n || v>n || adj[u][v]==0)
     {
printf("This edge does not exist\n");
return;
     }
     adj[u][v]=0;
}/*End of del_edge()*/