Calculator.cpp

//Description: A basic calculator for +, -, *, /, mod, square and squareroot

#include <iostream>
#include <cmath>
#include <cstdlib> // For holding output
#include <windows.h>
using namespace std;

int options;
float val1, val2;

// Function for invalid input like abc
float getNumber()
{
    float num;

    while (true)
    {
        cin >> num;

        if (!cin.fail())
        {
            return num;
        }

        cout << "Invalid number.\nPlease enter digits(e.g. 123): ";

        cin.clear();
        cin.ignore(1000, '\n');
    }
}

// Function for factorial
long long factorial(int n)
{
    if (n <= 1)
    {
        return 1;
    }
    return n * factorial(n - 1);
}

void opt()
{
    cout << "Choose your operation:\n1. Addition\n2. Subtracion\n3. Multiplication\n4. Division\n5. Remainder\n6. Square root\n7. Square\n8. Factorial\n0. Exit" << endl;
    cin >> options;
}

void value1()
{
    cout << "Enter your first value:" << endl;
    val1 = getNumber();
    cout << "Enter your second value:" << endl;
    val2 = getNumber();
}

void value2()
{
    cout << "Enter your value:" << endl;
    val1 = getNumber();
}

void sum()
{
    cout << val1 << " + " << val2 << " = " << val1 + val2 << endl;
}

void sub()
{
    cout << val1 << " - " << val2 << " = " << val1 - val2 << endl;
}

void mul()
{
    cout << val1 << " X " << val2 << " = " << val1 * val2 << endl;
}

void div()
{
    cout << val1 << " ÷ " << val2 << " = " << val1 / val2 << endl;
}

void mod()
{
    cout << val1 << " mod " << val2 << " = " << int(val1) % int(val2) << endl;
}

void sroot()
{
    cout << "√" << val1 << " = " << sqrt(val1) << endl;
}

void squ()
{
    cout << val1 << "² " << " = " << val1 * val1 << endl;
}

void fac()
{
    cout << val1 << "! " << " = " << factorial(val1) << endl;
}

int exit()
{
    cout << "Thank you for using the calculator!" << endl;
    system("pause");
}

int main()
{
    SetConsoleOutputCP(CP_UTF8);
    while (true) // Return to the "Choose your operation" after done with any operation
    {
        system("cls"); // To clear screen after every operation
        cout << "Name: Calculator" << endl;
        cout << "Version: 1.6" << endl;
        cout << "Author: Mr.AJ" << endl;
        cout << "Date: 06/03/2026" << endl;
        cout<<"\n\n";
        
        opt();
        cout<<"\n\n";

        if (cin.fail())
        {
            cout << "Please choose the number from 0 to 8" << endl;

            cin.clear();
            cin.ignore(1000, '\n');

            system("pause");
            continue;
        }

        // For closing calculator
        if (options == 0)
        {
            exit();
            return 0;
        }

        // For operation that requires two values(e.g. 5 + +)
        if (options >= 1 && options <= 5)
        {
            value1();
            // For Sum
            if (options == 1)
            {
                cout << "\n";
                sum();
            }

            // For subtraction
            else if (options == 2)
            {
                cout << "\n";
                sub();
            }

            // For multiplication
            else if (options == 3)
            {
                cout << "\n";
                mul();
            }

            // For division
            else if (options == 4)
            {
                // if user enters 0 in denominator
                if (val2 == 0.0f)
                {
                    cout<<"Error: Division by 0 is not allowed"<<endl;
                }
                else
                {
                    cout << "\n";
                    div();
                }
            }

            // For Remainder/mod
            else if (options == 5)
            {
                if (val2 == 0.0f) // if user enters 0 in denominator
                {
                    cout<<"Error: Division by 0 is not allowed"<<endl;
                }
                else
                {
                    cout << "\n";
                    mod();
                }
            }
        }

        // For operation that requires one value
        else if (options >= 6 && options <= 8)
        {
            value2();

            // For Square root
            if (options == 6)
            {
                // if user enter negative number
                if (val1 < 0)
                {
                    cout<<"Please choose positive numbers"<<endl;
                }
                else
                {
                    cout << "\n";
                    sroot();
                }
            }

            // For square
            else if (options == 7)
            {
                cout << "\n";
                squ();
            }

            // For Factorial
            else if (options == 8)
            {
                if (val1 < 0) // If user enter negative value
                {
                    cout<<"Please choose positive numbers"<<endl;
                }

                else if (val1 > 20) // For factorial, the value greater than 20 can create an error so we create a limit
                {
                    cout << "Maximum possible value is 20" << endl;
                }

                else if (val1 != int(val1)) // If user enter float value
                {
                    cout<<"Factorial works only with whole numbers"<<endl;
                }

                else
                {
                    cout << "\n";
                    fac();
                }
            }
        }
        else
        {
            cout<<"Error: Please choose the numbers from 0 to 8"<<endl;
        }
        system("pause");
    }
}