#include<stdio.h>
#include<string.h>
#include<ctype.h>
#define MAX 100

typedef struct
{
    char s[MAX]; // Operator Stack
    char a[MAX]; //Infix Expression
    char b[MAX]; //Postfix Expression
    int tos; //Top of stack
    int postindex; //Index of Postfix. Don't ask why defined here. Just feeling like it :P
}infix;

void transfer(infix *t,char k)
{
    t->b[t->postindex]=k;
    t->postindex++;
}

int ipr(char a)
{
    if (a=='(')
        return 3;
    else if (a=='+'||a=='-')
        return 1;
    else if (a=='%'||a=='/'||a=='*')
        return 2;
}

int rpr(char a)
{
    if (a=='(')
        return 0;
    else if (a=='+'||a=='-')
        return 1;
    else if (a=='%'||a=='/'||a=='*')
        return 2;
}

int isempty(infix *t)
{
    if (t->tos==-1)
        return 1;
    else
        return 0;
}

void display(infix *t)
{
    int i;
    int n=(int)strlen(t->b);
    for(i=0;i<n;i++)
    {
        printf("%s",t->b[i]);
    }
}


void push(infix *t,char a)
{

        t->tos++;
        t->s[t->tos]=a;
}

void pop(infix *t,char k)
{
    if(k=='(')
    {
        t->tos--;
    }
    else
    {
        transfer(t,k);
        t->tos--;
    }
}

int isoperand(char a)
{
    if(a=='+'||a=='-'||a=='%'||a=='/'||a=='*'||a=='(')
        return 1;
    else
        return 0;
}



void convert(infix *t)
{
    int i;
    int n=(int)strlen(t->a);
    for(i=0;i<n;i++)
    {
        if(isoperand(t->a[i]))
        {
            if (isempty(t))
            {
                push(t,t->a[i]);
            }
            else if(ipr(t->a[i])>rpr(t->s[t->tos]))
            {
                push(t,t->a[i]);
            }
            else if(ipr(t->a[i])<rpr(t->s[t->tos]))
            {
                while(isempty(t)!=1||ipr(t->a[i])>rpr(t->s[t->tos]))
                {
                    pop(t,t->a[i]);
                }
                push(t,t->a[i]);
            }
            else if(t->a[i]==')')
            {
                while(t->s[t->tos]!='(')
                {
                    pop(t,t->a[i]);
                }

            }
            else
            {
                transfer(t,t->a[i]);
            }

        }
    }
}

void main()
{

    infix s;
    s.postindex=0;
    s.tos=-1;
    printf("Enter the infix expression\n");
    gets(s.a);
    convert(&s);
    printf("\nThe Postfix expression is \n");
    display(&s);
    getchar();
}