function solve() {

    let buttons = Array.from(document.getElementsByTagName('button'));
    let clearButton = buttons.splice(0, 1);

    let firstNumber = '';
    let secondNumber = '';
    let isItFirstNumber = true;
    let operator = '';
    let result = 0;

    buttons.forEach(button => {
        button.addEventListener('click', calculate)
    });

    clearButton[0].addEventListener('click', clear);


    function calculate(e) {
        let buttonValue = e.target.textContent;
        let expressionOutput = document.getElementById('expressionOutput');

        if (buttonValue === '=') {
            if (firstNumber !== '' && secondNumber !== '' && operator.length === 1) {
                switch (operator) {
                    case 'x':
                        result = Number(firstNumber) * Number(secondNumber);
                        break;
                    case '/':
                        result = Number(firstNumber) / Number(secondNumber);
                        break;
                    case '-':
                        result = Number(firstNumber) - Number(secondNumber);
                        break;
                    case '+':
                        result = Number(firstNumber) + Number(secondNumber);
                        break;
                }
            } else {
                result = NaN;
            }

            document.getElementById('resultOutput').textContent = result;

        } else if (buttonValue >= '0' && buttonValue <= '9' || buttonValue === '.') {
            if (isItFirstNumber) {
                firstNumber += buttonValue;
            } else {
                secondNumber += buttonValue;
            }
            expressionOutput.textContent += buttonValue;
        } else {
            isItFirstNumber = false;
            operator += buttonValue;
            expressionOutput.textContent += ` ${buttonValue} `;
        }
    }

    function clear() {
        document.getElementById('resultOutput').textContent = '';
        document.getElementById('expressionOutput').textContent = '';
    }
}