Postfix ev

#include <stdio.h>

#include <ctype.h>

char stack[20];

int top = -1;

void push(char x)

{

    stack[++top] = x;

}

char pop()

{

    if (top == -1)

        return -1;

    else

        return stack[top--];

}

int priority(char x)

{

    if (x == '(')

        return 0;

    if (x == '+' || x == '-')

        return 1;

    if (x == '*' || x == '/')

        return 2;

    if (x == '^')

        return 3;

}

void main()

{

    char exp[20], x;

    printf("Enter expression: ");

    scanf("%s", exp);

    printf("Postfix expression: ");

    for (int i = 0; exp[i] != '\0'; i++)

    {

        if (isalnum(exp[i]))

            printf("%c", exp[i]);

        else if (exp[i] == '(')

            push(exp[i]);

        else if (exp[i] == ')')

        {

            while ((x = pop()) != '(')

                printf("%c", x);

        }

        else

        {

            while (priority(stack[top]) >= priority(exp[i]))

                printf("%c", pop());

            push(exp[i]);

        }

    }

    while (top != -1)

        printf("%c", pop());

}