evalpostfix.c

#include<stdio.h>
#include<conio.h>
#include<ctype.h>
void main()
{  static int a[5];
   int i,n,top=-1,op1,op2,noperator=0,noperand=0;
   char ch[10];
   clrscr();
   printf("\n Enter the string\n");
   gets(ch);
   for(i=0;ch[i]!='\0';i++)
  {
     if ((ch[i]>=48)&&(ch[i]<=57))
     {
       a[++top]=ch[i]-48;
       noperand++;
     }
   else
   switch(ch[i])

  {

    case '+' :      noperator++;
		    op2=a[top--];
		    op1=a[top--];
		    n=op1+op2;
		    a[++top]=n;
		    break;

    case '-' :      noperator++;
		    op2=a[top--];
		    op1=a[top--];
		    n=op1-op2;
		    a[++top]=n;
		    break;

    case '*' :      noperator++;
		    op2=a[top--];
		    op1=a[top--];
		    n=op1*op2;
		    a[++top]=n;
		    break;

    case '/' :      noperator++;
		    op2=a[top--];
		    op1=a[top--];
		    n=op1/op2;
		    a[++top]=n;
		    break;

    }

  }

  if(noperator==noperand-1)
    printf("value of the given expression is : %d",a[0]);
  else
    printf("\n Enter a correct postfix expression");
  getch();
 }