C Program to Convert an Infix Expression into a Postfix Expression

#include<stdio.h>
#include<conio.h>
#define MAX 50

int main()
{
   char a[100],b[MAX],ch;
   int top,i;
   clrscr();
   top=-1;
   printf("\nEnter Infix - \n");
   gets(a);
   
   for(i=0;a[i]!='\0';i++)
   {
 if (a[i]=='(')
 {
  push(b,&top,&a[i]);
 }
 else if (a[i]==')')
 {
  
  while(b[top]!= '(')
  {
   pop(b,&top,&ch);
   printf("%c",ch);
  }
  pop(b,&top,&ch); 
 }
 else
 if (check(a[i])==0) 
  printf("%c",a[i]);
 else 
 {
  if(top==-1)  
  {
   push(b,&top,&a[i]);
  }
  else
  if (priority(a[i]) > priority(b[top]))
  {
   push(b,&top,&a[i]);
  }
  else
  {
   while (priority (a[i])<=priority(b[top]))
   {
    if (top == -1)
     break;
    pop(b,&top,&ch);
    printf("%c",ch);
   }
   push(b,&top,&a[i]);
  }
 }
   }
   while(top!=-1)
   {
 pop(b,&top,&ch);
 printf("%c",ch);
   }
}

int check(char ch)
{
 switch(ch)
 {
  case '^':
  case '*':
  case '/':
  case '%':
  case '+':
  case '-': return(1);
  default : return(0);
 }
}

int priority(char opt)
{
 switch(opt)
 {
  case '^' : return(4);
  case '*' :
  case '/' :
  case '%' : return(3);
  case '+' :
  case '-' :return(2);
  case '(' : return(1);
  default : return (0);
 }
}

int push(char b[MAX],int *top,char *ch)
{
 if(*top==MAX-1)
 {
  return(-1);
 }
 else
 {
  (*top)++;
  b[*top]=*ch;
  return(1);
 }
}

int pop(char b[MAX],int *top,char *ch)
{
 if (*top==-1)
 {
  return(-1);
 }
 else
 {
  *ch=b[*top];
  (*top)--;
  return(1);
 }
}