postfix.c

#include<stdio.h>
#include<string.h>
#define MAX 50
int stack[MAX];
char post[MAX];
int top=-1;
void pushstack(int tmp);
void evaluate(char c);
void main()
{
    int i,l;
    printf("Insert a postfix notation :: ");
    gets(post);
    l=strlen(post);
    for(i=0; i<l; i++)
    {
        if(post[i]>='0' && post[i]<='9')
        {
            pushstack(i);
        }
        if(post[i]=='+' || post[i]=='-' || post[i]=='*' ||
                post[i]=='/' || post[i]=='^')
        {
            evaluate(post[i]);
        }
    }
    printf("\n\nResult :: %d",stack[top]);
}
void pushstack(int tmp)
{
    top++;
    stack[top]=(int)(post[tmp]-48);
}
void evaluate(char c)
{
    int a,b,ans;
    a=stack[top];
    stack[top]='\0';
    top--;
    b=stack[top];
    stack[top]='\0';
    top--;
    switch(c)
    {
    case '+':
        ans=b+a;
        break;
    case '-':
        ans=b-a;
        break;
    case '*':
        ans=b*a;
        break;
    case '/':
        ans=b/a;
        break;
    case '^':
        ans=b^a;
        break;
    default:
        ans=0;
    }
    top++;
    stack[top]=ans;
}