cal.ts

import { question } from "readline-sync";

type Operator = '+' | '-' | '*' | '/';

function main(): void
{
    const firstStr: string = question('Enter first number:\n');
    const operator: string = question('Enter operator:\n');
    const secondStr: string = question('Enter second number\n');

    const validInput: boolean = isNumber(firstStr) && isOperator(operator) && isNumber(secondStr);

    if (validInput)
    {
        const firstNum: number = parseInt(firstStr);
        const secondNum : number = parseInt(secondStr);
        const result = calculate(firstNum, operator as Operator, secondNum);
        console.log(result);
    }
    else
    {
        console.log('\ninvalid input\n');
        main()
    }
}

function calculate(firstNum: number, operator: Operator, secondNum: number)
{
    switch(operator)
    {
        case '+':
            return firstNum + secondNum;
        case '-':
            return firstNum - secondNum;
        case '*':
            return firstNum * secondNum;
        case '/':
            return firstNum / secondNum;            
    }
}

function isOperator(operator: string): boolean
{
    switch(operator)
    {
        case '+':
        case '-':
        case '*':
        case '/':
            return true;  
        default:
            return false;  
    }
}


function isNumber(str: string): boolean
{
    const maybeNum = parseInt(str);
    const isNum: boolean = !isNaN(maybeNum);
    return isNum
}

main();