function appendValue(val) {
    document.getElementById("result").value += val;
}

function clearResult() {
    document.getElementById("result").value = "";
}

function calculate() {
    try {
        let exp = document.getElementById("result").value;
        document.getElementById("result").value = eval(exp);
    } catch {
        document.getElementById("result").value = "Error";
    }
}