Calculator in C++ or how to solve the problem with actions?

Question

C++ / C#

Hello dear!
I started learning functions .. and immediately decided to make a calculator using functions ..
Problem: when I made a choice, for example, 16 / 4 gives out which is 20.

If you have free time, help explain what the problem is

#include <iostream>
using namespace std;

void title() {
    cout << "КАЛЬКУЛЯТОР\tby Chorrny Edition" << endl;
}

int Function1(int a, int b) {
    return a + b;
}
int Function2(int a, int b) {
    return a - b;
}
int Function3(int a, int b) {
    return a * b;
}
int Function4(int a, int b) {
    return a / b;
}
int main()
{
    setlocale(LC_ALL, "");

    int res, a, b;
    int choise = 0;
    title();
    cout << "Выберите действие:\n\t 1 - добавления:\n\t 2 - вычитание:\n\t 3 - умножение:\n\t 4 - Деление:" << endl;
    cin >> a;
    cout << "Первая цифра -->";
    cin >> b;
    cout << "Вторая цифра -->";
    cin >> choise;
    if (choise == 1) {
        res = Function1(a, b);
    }
    else if (choise == 1) {
        res = Function2(a, b);
    }
    else if (choise == 1) {
        res = Function3(a, b);
    }
    else if (choise == 1) {
        res = Function4(a, b);
    }

    cout << res << "Результат: "; 
    system("pause");
    return 0;
}

Thank you!

Answer 1

You are always folding, regardless of the user's choice.
Change the if block to this one:

if (choise == 1) {
  res = Function1(a, b);
}
else if (choise == 2) {
  res = Function2(a, b);
}
else if (choise == 3) {
  res = Function3(a, b);
}
else if (choise == 4) {
  res = Function4(a, b);
}

I also advise you to give function names more meaningful ( add , subtract, mul , div)

Answer 2

#include
using namespace std;
void title() {
cout << "CALCULATOR\tby Chorrny Edition" << endl;
}
int Function1(int a, int b) {
return a + b;
}
int Function2(int a, int b) {
return a - b;
}
int Function3(int a, int b) {
return a * b;
}
int Function4(int a, int b) {
return a / b;
}
int main()
{
setlocale(LC_ALL, "");
int res, a, b;
int choice = 0;
title();
cout << "Select action:\n\t 1 - add:\n\t 2 - subtract:\n\t 3 - multiply:\n\t 4 - divide:" << endl;
cin >> choose;
cout << "First digit -->";
cin >> a;
cout << "Second digit -->";
cin >> b;
if (choise == 1)
{
res = Function1(a, b);
}
else if (choise == 2)
{
res = Function2(a, b);
}
else if (choise == 3) {
res = Function3(a, b);
}
else if (choise == 4) {
res = Function4(a, b);
}
cout << "Result: "<< res < system("pause");
return 0;
}

Answer 3

using channing Method
#include
using namespace std;
/**
* @brief Method chaining
* @tparam T
*/
template
class Mathem {
public:
Mathem(T xx):m_value(xx){};
Mathem& add(T value){m_value+=value; return *this; }
Mathem& sub(T value){m_value-=value; return *this; }
Mathem& multiply(T value){m_value*=value; return *this; }
int getValue(){return m_value;}
operator T(){return m_value;}
private:
int m_value;
};
int main(){
Mathem operation(2);
operation.add(2).sub(3).multiply(5);
cout<
}