#include<stdio.h>
#include<ctype.h>
#define max 50
char infix[max],postfix[max],s[max],elem;
int i,j=0,top=-1;
void push(char operator);
char pop();
void convert();
int priority(char operator);
int main()
{
printf("Enter infix expression\n");
scanf("%s",infix);
convert();
return 0;
}
void push(char operator)
{
if(top==max-1)
printf("STACK OVERFLOW\n");
else
{
top++;
s[top]=operator;
}
}
char pop()
{
if(top==-1)
printf("STACK UNDERFLOW\n");
else
return s[top--];
}
int priority(char operator)
{
switch(operator)
{
case'^':return 3;
case'*':
case'/':
case'%':return 2;
case'+':
case'-':return 1;
case'(':return 0;
case'#':return -1;
default: printf("Invalid Operator\n");
}
}
void convert()
{
push('#');
for(i=0;infix[i]!='\0';i++)
{
switch(infix[i])
{
case'(':push('(');
break;
case'^':
case'*':
case'/':
case'%':
case'+':
case'-':
        while(priority(s[top])>=priority(infix[i]))
{
elem=pop();
        postfix[j++]=elem;
}
push(infix[i]);
break;

case')':while((elem=pop())!='(')	//check
{
postfix[j++]=elem;
}
break;
default:if(isalnum(infix[i]))
postfix[j++]=infix[i];
else
printf("Invalid operand\n");
break;
}
}
while((elem=pop()!='#'))
{
postfix[j++]=elem;
postfix[j]='\0';
printf("Postfix expression=%s\n",postfix);
}
}