gcd==1 in the if statement does not make it true even if you enter e with the appropriate value.

#include<stdio.h>
# include <math.h>

int gcd(intf, inte){

  intr;

  while(r!=0){
    r = f%e;
    f=e;
    e=r;
  }

  return f;

}

int main(void){

int hirabun;
intp;
intq;
int flag = 0;
inti;
intn;
inte;
intf;
intr;

printf("Please enter a plaintext number:");
scanf("%d", & hirabun);
printf("Please enter p:");
scanf("%d", &p);
printf("Please enter q:");
scanf("%d", & q);
for(i=2;i<p;++i){
   if(p%i==0){
     flag = 1;
     break;
   }
 }

 if(flag==0)
   printf("%d is a prime number.\n", p);
 else
   printf("%d is not a prime number.\n", p);

// return 0;

 for(i=2;i<q;++i){
    if(q%i==0){
      flag = 1;
      break;
    }
  }

  if(flag==0)
    printf("%d is a prime number.\n",q);
  else
    printf("%d is not a prime number.\n",q);



  n = p*q;
  f = (p-1)*(q-1);



  printf("gcd(f,e)=Enter an e with 1 :");
  scanf("%d", & e);
  if(gcd(f,e)==1)
   printf("gcd(f,e)=1\n";
  else
   printf("No, it's not.");
   return 0;

  printf("e value is %d",e);
  printf("%d", gcd(f,e)));

}