//Global letiables
let prevCalc = 0;
let calc = "";

//The following function displays a number in the textfield when a number is clicked.
//Note that it keeps concatenating numbers which are clicked.
function showNum(value) {
    document.frmCalc.txtNumber.value += value;
}

//The following function decreases the value of displayed number by 1.
//isNaN method checks whether the value passed to the method is a number or not.
function decrement() {
    let num = parseFloat(document.frmCalc.txtNumber.value);
        if (!(isNaN(num))) {
            num--;
            document.frmCalc.txtNumber.value = num;
        }
}

//The following function is called when "Add" button is clicked.
//Note that it also changes the values of the global letiables.
function add() {
    let num = parseFloat(document.frmCalc.txtNumber.value);
        if (!(isNaN(num))) {
            prevCalc = num;
            document.frmCalc.txtNumber.value = "";
            calc = "Add";
        }
}

// Subtraction function
function subtract(){
    let num = parseFloat(document.frmCalc.txtNumber.value);
        if (!(isNaN(num))) {
            prevCalc = num;
            document.frmCalc.txtNumber.value = "";
            calc = "Subtract";
        }
}

// Square root function
function sqrt(){
     let num = parseFloat(document.frmCalc.txtNumber.value);
        if (!(isNaN(num))) {
            num = Math.sqrt(num);
            document.frmCalc.txtNumber.value = num;
            prevCalc = num;
        }
}

//The following function is called when "Calculate" button is clicked.
//Note that this function is dependent on the value of global letiable.
function calculate() {
    let num = parseFloat(document.frmCalc.txtNumber.value);
        if (!(isNaN(num))) {
            if (calc == "Add"){
                let total = prevCalc + num;
                document.frmCalc.txtNumber.value = total;
            }else if(calc == "Subtract"){
                let total = prevCalc - num;
                document.frmCalc.txtNumber.value = total;
            }
        }

}

function clear() {
    document.frmCalc.txtNumber.value = "";
    prevCalc = 0;
    calc = "";
}



// Implement floor() and round()

// Square root function
function floor(){
     let num = parseFloat(document.frmCalc.txtNumber.value);
        if (!(isNaN(num))) {
            num = Math.floor(num);
            document.frmCalc.txtNumber.value = num;
            prevCalc = num;
        }
}

// Square root function
function round(){
     let num = parseFloat(document.frmCalc.txtNumber.value);
        if (!(isNaN(num))) {
            num = Math.round(num);
            document.frmCalc.txtNumber.value = num;
            prevCalc = num;
        }
}