How to make a simple calculator

This page is about creating a simple calculator. A good way to do this is to first ask for what kind of operation to do, then ask the first variable, and then the second.

Examples

C++

#include <iostream>
#include <cstdlib>

using namespace std;

int main()
	{
	double num1, num2;
        int opselect;

        cout << "\n welcome.";
        cout << "this is a simple calculator.";
        cout << "\n enter the first number: ";
        cin >> num1;
        cout << "enter operation: ";
        cout << "\n  1 = addition";
        cout << "\n  2 = subtraction";
        cout << "\n  3 = multiplication";
        cout << "\n  4 = division";
        cout << "\n  - ";
        cin >> opselect;
        cout << "enter the second number: ";
        cin >> num2;

        cout << "CALCULATING";
        cout << ".";
        cout << ".";
        cout << ".";

      if (num1 == 2, num2 == 2, opselect == 1)
         {
         cout << num1 << " + " << num2 << " = " << "chair" << endl;
         }
     else
     	switch (opselect)
     		{
                case 1:
		        cout << num1 << " + " << num2 << " = " << num1+num2 << endl;
            		break;
                case 2:
			cout << num1 << " - " << num2 << " = " << num1-num2 << endl;
			break;
                case 3:
                        cout << num1 << " X " << num2 << " = " << num1*num2 << end;
                        break;
                case 4:
			cout << num1 << " / " << num2 << " = " << num1/num2 << endl;
			break;
            }
    system("PAUSE");
	return 0;
}

From ProgrammingWiki, a Wikia wiki.

Java

An open source calculator:

import java.util.Scanner;
public class Main {
    public static void main(String[] args) {
        System.out.println("DOS-CALC::Created by AntoArts Entertainment");
        System.out.println("----------------v1.0.00--------------------");
        Scanner scan = new Scanner(System.in);
        System.out.println("Type the name of the operation you want to use: ");
        System.out.println(" (addition/subtraction/multiplication/division)");
        String operat = scan.next();
        if(operat.equals("addition")){
            System.out.println("Counting with addition, please type in variable A: ");
            double a = scan.nextDouble();
            System.out.println("Variable A is "+a+", please type in variable B: ");
            double b = scan.nextDouble();
            double z=a+b;
            System.out.println(a+"+"+b+"="+z);
        }
        else if(operat.equals("subtraction")){
            System.out.println("Counting with subtraction, please type in variable A: ");
            double a = scan.nextDouble();
            System.out.println("Variable A is "+a+", please type in variable B: ");
            double b = scan.nextDouble();
            double z=a-b;
            System.out.println(a+"-"+b+"="+z);
        }
        else if(operat.equals("multiplication")){
            System.out.println("Counting with multiplication, please type in variable A: ");
            double a = scan.nextDouble();
            System.out.println("Variable A is "+a+", please type in variable B: ");
            double b = scan.nextDouble();
            double z=a*b;
            System.out.println(a+"*"+b+"="+z);
        }
        else if(operat.equals("division")){
            System.out.println("Counting with division, please type in variable A: ");
            double a = scan.nextDouble();
            System.out.println("Variable A is "+a+", please type in variable B: ");
            double b = scan.nextDouble();
            double z=a/b;
            System.out.println(a+"/"+b+"="+z);
        }
        else{
            System.out.println("The operation you've requested wasn't avaiable");
            System.out.println("Check spelling and make sure you typed the operation name lowercase");
        }
    }
}

Lua

-- Operators that the user will use.
local operators = {
    ["+"] = function(x, y) return x + y end,
    ["-"] = function(x, y) return x - y end,
    ["*"] = function(x, y) return x * y end,
    ["/"] = function(x, y) return x / y end
}

-- Error if the operator was not in the operator "list"
local function operatorError()
    print "No such operator"
end

-- The input part of the calculator
print("Numbers:")
print("Enter first number:")
local number1 = io.read()
print("Enter second number:")
local number2 = io.read()
print("Enter operator: + / - / * / /")

-- The output part of the calculator
local func = operators[io.read()] or operatorError
print(func(number1, number2))

See Also

• Mathematical functions