Postfix Evaluation

PROGRAM:

#include<stdio.h>
#include<string.h>
#include<conio.h>
void push(int);
int pop();
int stack[20],top=-1;
void main()
{
 char expr[20];
 int len,a,b,c,i,x;
 clrscr();
 printf("$$$ POSTFIX EVALUATION $$$");
 printf("\nEnter the postfix expression:");
 scanf("%s",expr);
 len=strlen(expr);
 for(i=0;i<len;i++)
 {
  if(expr[i]=='+'||expr[i]=='-'||expr[i]=='*'||expr[i]=='/')
  {
   b=pop();
   a=pop();
   switch(expr[i])
   {
    case '+':c=a+b;
      push(c);
      break;
    case '-':c=a-b;
      push(c);
      break;
    case '*':c=a*b;
      push(c);
      break;
    case '/':c=a/b;
      push(c);
      break;
   }
  }
  else
  {
   printf("Enter the value of %c:",expr[i]);
   scanf("%d",&x);
   push(x);
  }
 }
 printf("The resultant value is : %d",stack[top]);
 getch();
}
void push(int item)
{
 stack[++top]=item;
}
int pop()
{
 int a;
 a=stack[top];
 top=top-1;
 return a;
}


OUTPUT:

$$$ POSTFIX EVALUATION $$$

Enter the postfix expression: abc+*
Enter the value of a: 10
Enter the value of b: 20
Enter the value of c: 30
The resultant value is : 500