infix and postfix

#include<stdio.h>

#include<ctype.h>

char stack[100];

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;

    return 0;

}

int main()

{

    char exp[100];

    char *e, x;

    printf("Enter the expression : ");

    scanf("%s",exp);

    printf("\n");

    e = exp;

    printf("Postfix expression : ");

    while(*e != '\0')

    {

        if(isalnum(*e))

            printf("%c ",*e);

        else if(*e == '(')

            push(*e);

        else if(*e == ')')

        {

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

                printf("%c ", x);

        }

        else

        {

            while(priority(stack[top]) >= priority(*e))

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

            push(*e);

        }

        e++;

    }

    while(top != -1)

    {

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

    }return 0;

}