While Loop

#include <iostream>
#include <conio.h>
#include <ctype.h>
#include <string>
#include <array>
using namespace std;
int Addition(int x,int y);
int Subtraction(int x,int y);
int Multiplication(int x,int y);
int Division(int x,int y);

void main(){
    int x = 0;
    while( x == 0 ){
    int num1;
    string oper;
    int num2;

    cout << "******************************************" << endl;
    cout << "*       Welcome to C++ Calculator        *" << endl;
    cout << "*                   By                   *" << endl;
    cout << "*                ryan7136                *" << endl;
    cout << "******************************************" << endl;
    cout << "*       Please enter an operation:       *" << endl;
    cout << "*            Your choices are:           *" << endl;
    cout << "*  add, subtract, multiply, divide, pi,  *" << endl;
    cout << "*                 and exit               *" << endl;
    cout << "******************************************" << endl;

    getline(cin , oper);
    cin.clear();

    if(oper == "add"){
    cout << "Enter the first number:";
    cin >> num1;
    cout << "Enter the second number:";
    cin >> num2;
    cout << "The sum is: " << Addition(num1,num2) << "." << endl;
    }
    if(oper == "subtract"){
    cout << "Enter the first number:";
    cin >> num1;
    cout << "Enter the second number:";
    cin >> num2;
    cout << "The sum is: " << Subtraction(num1,num2) << "." << endl;
    }
    if(oper == "multiply"){
    cout << "Enter the first number:";
    cin >> num1;
    cout << "Enter the second number:";
    cin >> num2;
    cout << "The sum is: " << Multiplication(num1,num2) << "." << endl;
    }
    if(oper == "divide"){
    cout << "Enter the first number:";
    cin >> num1;
    cout << "Enter the second number:";
    cin >> num2;
    cout << "The sum is: " << Division(num1,num2) << "." << endl;
    }
    if(oper == "pi"){
    cout << "pi: 3.14159265358979323846264338327950288" << endl;
    }
    if(oper == "exit"){
    int x = 12;
    }
    system("CLS");
    }
}


int Addition(int x, int y){
    int answer;
    answer = x + y;
    return answer;
}
int Subtraction(int x, int y){
    int answer;
    answer = x - y;
    return answer;
}
int Multiplication(int x, int y){
    int answer;
    answer = x * y;
    return answer;
}
int Division(int x, int y){
    int answer;
    answer = x / y;
    return answer;
}