function solve() {
    let operands = ["/", "*", "-", "+",];
    let resultStr = "";
    let operator;
    let buttons = document.getElementsByTagName("button");
    Array.from(buttons).map(x => x.addEventListener("click", function calc(e) {
        let btn = e.target.value;
        if (btn === "Clear") {
            resultStr = undefined;
            resultStr = "";
            document.getElementById("expressionOutput").innerHTML = resultStr;
            document.getElementById("resultOutput").innerHTML = resultStr;
        }
        else if (operands.includes(btn)) {
            operator = btn;
            resultStr += ` ${operator} `;
            document.getElementById("expressionOutput").innerHTML = resultStr;
        }
        else if (btn === "=") {
            let val = resultStr.split(operator).map(x => x.trim()).filter(x => x != "");
            if (val.length === 1) {
                resultStr = "NaN";
            }
            else {
                switch (operator) {
                    case "/": resultStr = Number(val[0]) / Number(val[1]); break;
                    case "*": resultStr = Number(val[0]) * Number(val[1]); break;
                    case "+": resultStr = Number(val[0]) + Number(val[1]); break;
                    case "-": resultStr = Number(val[0]) - Number(val[1]); break;
                }
            }
            document.getElementById("resultOutput").innerHTML = resultStr;
        }
        else {
            resultStr += btn;
            document.getElementById("expressionOutput").innerHTML = resultStr;
        }
    }))
}