postfix_expression_evaluation.c

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

#define size 100
int stack[size];
int top = -1;

void push(int x)
{
    if(top == size-1)
    {
        printf("Stack Overflow\n");
    }
    
    else
    {
        stack[++top] = x;
    }
}

int pop()
{
    if(top == -1)
    {
        return 0;
    }

    else
    {
        int ele;
        ele = stack[top--];
        return ele;
    }
}

int main()
{
    char arr[50];
    int i=0, op1, op2;
    printf("Enter the Postfix expression\n");
    scanf("%s",arr);

    for(i=0; arr[i]!='\0'; i++)
    {
        if(isdigit(arr[i]))
        {
            push(arr[i]-'0');
        }

        else
        {
            op2 = pop();
            op1 = pop();

            switch(arr[i])
            {
                case '+':
                    push(op1 + op2);
                    break;

                case '-':
                    push(op1 - op2);
                    break;

                case '*':
                    push(op1 * op2);
                    break;

                case '/':
                    push(op1 / op2);
                    break;

                case '^':
                    push(op1 ^ op2);
                    break;

                default:
                    printf("\nInvalid operation\n");
                    break;
            }
        }
    }

    printf("\nThe result is %d",stack[top]);
    
    return 0;
}