Infix into postfix

#include<stdio.h>
#include<conio.h>
#define max 100
#include<ctype.h>
#include<string.h>
#include<stdlib.h>

int isoper(char ch);
int precedence(char);
int main()
{
      int i,j=0,len;
char infix[max],postfix[max], stack[max];
int top=-1;
   printf(" Enter infix");
   gets(infix);
   len=strlen(infix);
   for (i=0; i<len; i++)
   {  //opening of for loop
if(isalpha(infix[i]))
postfix[j++]=infix[i];
else if(isoper(infix[i]))
{ //opening of else if
while(top>-1 && stack[top]!='(')
{    //opening of while loop
  if(precedence(infix[i])<=precedence(stack[top]))
{  //opening of if
postfix[j++]=stack[top--];
}// closing of if
else break;
}//closing of while

stack[++top]=infix[i];
} //closing of else if
else if(infix[i]=='(')
stack[++top]=infix[i];

else if(infix[i]==')')
      {       while (stack[top]!='(')
     { postfix[j++]=stack[top--];
     }
top--;

}
     }//closing for loop
   while (top>-1)
   postfix[j++]=stack[top--];
   postfix[j++]='\0';
   printf("Infix expression %s", infix);
   printf("\n postfix expression %s", postfix);

   getch();
}// closing main

int precedence(char ch)
{
int prcd;
if(ch=='+'|| ch == '-')
prcd=0;
else if(ch=='*'|| ch=='/')
prcd=1;
else if(ch=='$')
prcd=2;
else
{
printf("Invalid operator");
exit(0);
}
return prcd;
}
int isoper(char ch)
{
if(ch=='+' || ch=='-'|| ch=='*' || ch== '/'|| ch=='$')
return 1;
else
return 0;
}


OUTPUT

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