Infix - Postfix.c

#include <stdio.h>
#include <stdlib.h>
#include<ctype.h>
char stack[20];
int top =-1;
void push(char x)    //function push initiated
{
	stack[++top]=x;
}
char pop()             //function pop initiated
{
	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;
}
int main()
{
	char exp[20];
	char *e, x;
	printf("Enter the expression: \n");
	scanf("%s", exp);
	e = exp;
	printf("The poftfix expression\n");
	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());
	}
}