program to evaluate a prefix expression using stack

.

#include<stdio.h>

#include<conio.h>

#include<stdlib.h>

main()

{

      char s[80];

      int stack[80],n,top=-1,x=0,y=0,i;

      printf("Enter postfix expression=");

      gets(s);

      n=strlen(s);

      for(i=n;i>=0;i--)

      {

            switch(s[i])

            {

                  case '+':

                  x=stack[top];

                  y=stack[top-1];

                  top=top-1;

                  x=x+y;

                  stack[top]=x;

                  break;

                  case '-':

                  x=stack[top];

                  y=stack[top-1];

                  top=top-1;

                  x=x-y;

                  stack[top]=x;

                  break;

                  case '*':

                  x=stack[top];

                  y=stack[top-1];

                  top=top-1;

                  x=x*y;

                  stack[top]=x;

                  break;

                  case '/':

                  x=stack[top];

                  y=stack[top-1];

                  top=top-1;

                  x=x/y;

                  stack[top]=x;

                  break;

                  default:

                  top=top++;

                  if(s[i]>=48&&s[i]<=57)

                  x=s[i]-48;

                  stack[top]=x;

                  break;

            }

      }

      printf("The result is=%d",stack[top]);

      getch();

}