infix_to_postfix_using_stack.c

#include<stdio.h>
#include<ctype.h>
#include<stdlib.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;
}
int main()
{
   char exp[20];
   char *e,x;
   printf("\nenter the infix expresion\n");
   scanf("%s",exp);
   e=exp;
   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;
}