为什么这段代码提前退出?

    #include <stdio.h>
    #define MAX 5
    int stk[MAX];
    int top=-1;

    main() 
     {
      char ch;
      void push();
      void pop();
     void display();

     do
     {
      printf("1. Push\n");
      printf("2. Pop\n");
      printf("3. Display\n");
      ch=getchar();

         if(ch=='1')
            push();
         if(ch=='2')
            pop();
         if(ch=='3')
            display();

    printf("Do u want to continue y/n"); 
    ch=getchar();
       }while(ch=='y'||ch=='Y');

    }

void push()
 {
   }

void pop()
 {
   }

void display()
 {
   }
    #include <stdio.h>
    #define MAX 5
    in