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Javascript – showing the sum of the digits in JS

I get a number from the user and i want to calculate the sum of its digits. here’s the code:

let num = Number(prompt("Enter a number to see the sum of its digits:"));
if (isNaN(num)) {
    alert("please enter a number");
} else {
    let sum = 0;
    for (let i = 0; i < num.length; i++) {
        sum = sum + num[i];
    }
    console.log(sum);
    alert("The result is : " + sum);
}

the program resulted in 0 number as the sum of digits and it’s, it’s just not working

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4

Answers


  1. 0

    You are converting the prompt input to a number and then trying to loop through the number as if it was an array (which it is not). Instead, leave the input as a string and loop over that array-like object and only convert the individual digits when doing the math.

    let num = prompt("Enter a number to see the sum of its digits:");

// Just check for input at this point. Doesn't matter yet if it's a number or not.
if (!num) {
    alert("please enter a number");
} else {
    let sum = 0;
    for (let i = 0; i < num.length; i++) {
        // The prepended + is an implicit way to convert a string to a number
        sum = sum + +num[i];
    }
    console.log(sum);
    alert("The result is : " + sum);
}
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  2. 0

    You cannot iterate on a variable which is of number type.
    The correct code will be :-

    let num = prompt("Enter a number to see the sum of its digits:");
if (!Number(num)) {
    alert("please enter a number");
} else {
    let sum = 0;
    for (let i = 0; i < num.length; i++) {
        sum = sum + num[i];
    }
    console.log(sum);
    alert("The result is : " + sum);
}
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  3. 0

    The reason it’s not working is because, during the loop, you’re basically treating num as if it was a string, but it’s actually always a number.

    Here’s a working code (without changing too much of your code):

    let num = Number(prompt("Enter a number to see the sum of its digits:"));
if (isNaN(num)) {
    alert("please enter a number");
} else {
    const numString = num.toString(); // Convert it to a string
    let sum = 0;
    for (let i = 0; i < numString.length; i++) {
        // Convert the char (string) to a number to make the sum work
        sum = sum + Number(numString.charAt(i));
    }
    console.log(sum);
    alert("The result is : " + sum);
}

    Note: in this case, .charAt() may be a little safer than the bracket notation, because it always returns a string (here’s a detailed explanation).

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  4. 0 
    function sumOfDigit(num) {
return num.toString().split("")
    .reduce((sum, digit) =>
        sum + parseInt(digit), 0);
}
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