function solve() {

    let regex = /^(\d+|\d+\.\d+) [/\-+x] (\d+|\d+\.\d+)$/g;

    let expressionOutput = document.querySelector('#expressionOutput');
    let resultOutput = document.querySelector('#resultOutput');
    let button = document.querySelector('.top .clear');
    let keys = Array.from(document.querySelector('.keys').children);

    console.log(keys);

    button.addEventListener('click', clear);

    keys.forEach(x => {
        x.addEventListener('click', function (e) {
            let key = e.target;

            if (key.textContent === '=') {

                let text = expressionOutput.textContent;
                if (validate(text)){
                    let first = text.indexOf(' ');
                    let second = text.lastIndexOf(' ');
                    let left = text.slice(0,first);
                    let right = text.slice(second + 1);
                    let operator = text[second - 1];
                    console.log(left);
                    console.log(right);
                    console.log(operator);

                    // resultOutput.textContent = ;
                }
                else {
                    resultOutput.textContent = 'NaN';
                }
            }
            else if (key.textContent === '*' || key.textContent === '-' || key.textContent === '+' || key.textContent === '/') {
                expressionOutput.textContent += ' ' + key.textContent + ' ';
            }
            else {
                expressionOutput.textContent += key.textContent;
            }
        })
    });

    function validate(text) {

        if (regex.test(text)){
            return true;
        }
       return false;
    }

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