lab5.c

// Design,Develop and implement a program in C for the following stack applications a.
// Evaluation of suffix expression with single digit operands and operators:+,-,*,/,^,%

#include<stdio.h>
#include<math.h>
#include<stdlib.h>
#include<ctype.h>


int s[20],top=-1;
int evaluate(char *);
void push(int);
int pop();
void main()
{
    int res;
    char post[30];
    printf("enter a valid postfix expression\n");
    scanf("%s",post);
    res=evaluate(post);
    printf("result of expression is %d",res);
    //getch();
}

int evaluate(char *post)
{
    int i,op1,op2,res,x;
    char sym;
    for(i=0;post[i]!='\0';i++)
    {
        sym=post[i];
        if(isalpha(sym))
        {
            printf("enter value for %c",sym);
            scanf("%d",&x);
            push(x);
        }
        else if (isdigit(sym))
        push(sym-'0');
        else{
            op2=pop();
            op1=pop();

            switch(sym)
            {
                case '+':res=op1+op2;
                break;
                case '-':res=op1-op2;
                break;
                case '*':res=op1*op2;
                break;
                case '/':res=op1/op2;
                break;
                case '^':res=pow(op1,op2);
                break;
                case '%':res=op1%op2;
                break;
                default:printf("Invalid operator in the expression is %c\n",sym);
                exit(0);
            }
            push(res);
        }
    }
    return(pop());
}


void push(int item)
{
    s[++top]=item;
}

int pop()
{
    return(s[top--]);
}