Infix to Postfix Line by Line

//           * * Bismillahir Rahmanir Rahim  * *
// ************************@Author*******************************
/*                    Asik Ifthaker Hamim                       */
#include <bits/stdc++.h>
#include<stdlib.h>
using namespace std;
typedef long long ll;
typedef unsigned long long int ulli;
typedef long long int lli;
typedef unsigned long long ull;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef vector<string> vs;
typedef pair<ll,ll> pr;
#define pb push_back
#define sz(n) n.size()
#define vs(n) (int)n.size()
#define pp pop_back
#define sp(n) setprecision(n)
#define big 1000000007
#define ffor(a, b) for (int i = a; i <b; i++)
#define frev(b, a) for (int i = b; i >= a; i--)
#define PI (acos(-1.0))
#define torad(x) ((x)*((2*acos(0))/180.0))
#define todeg(x) ((x)*(180.0/(2*acos(0))))
#define fixAngle(x) ((x)>1?1:(x)<-1?-1:(x))
#define tan(a) tan(a)/(pi/180)
#define sin(a) sin(a)/(pi/180)
#define cos(a) cos(a)/(pi/180)
#define inverse_sin(a) asin(a)/(pi/180)
#define inverse_cos(a) acos(a)/(pi/180)
#define inverse_tan(a) atan(a)/(pi/180)
#define eps 1e-9
const int dr4[] = {0, 1, 0, -1};
const int dc4[] = {1, 0, -1, 0};
const int dr8[] = {0, 1, 1, 1, 0, -1, -1, -1};
const int dc8[] = {1, 1, 0, -1, -1, -1, 0, 1};
using namespace std;
double neg_infinity(-std::numeric_limits<double>::infinity());
#define ran 1000000
#define MAX_SIZE 100

char Stack[MAX_SIZE];
int top = -1;

void push(char item)
{
    Stack[++top] = item;
}

char pop()
{
    return Stack[top--];
}

int priority(char symbol)
{
    switch(symbol)
    {
    case '+':
    case '-':
        return 1;
    case '*':
    case '/':
        return 2;
    case '^':
        return 3;
    default:
        return 0;
    }
}
int main()
{
    ios_base::sync_with_stdio(false);
    char infix[MAX_SIZE], postfix[MAX_SIZE];
    printf("Enter an infix expression: ");
    scanf("%s", infix);
    //infixToPostfix(infix, postfix);
    for(int k=00;k<1;k++)
    {
        int i, j;
        char item;
        push('(');
        strcat(infix, ")");
        i = j = 0;
        item = infix[i];
        while(item != '\0')
        {
            if(item == '(')
            {
                push(item);
            }
            else if(isalnum(item))
            {
                postfix[j] = item;
                j++;
            }
            else if(strchr("+-*/^", item) != NULL)
            {
                while(priority(Stack[top]) >= priority(item))
                {
                    postfix[j] = pop();
                    j++;
                }
                push(item);
            }
            else if(item == ')')
            {
                while(Stack[top] != '(')
                {
                    postfix[j] = pop();
                    j++;
                }
                pop();
            }
            else
            {
                //printf("Invalid expression");
                break;
            }
            i++;
            item = infix[i];
            postfix[j] = '\0';
            printf("Postfix expression: %s\n", postfix);

        }

        if(top > 0)
        {
            printf("Invalid expression");
        }

    }



}