JavaScript: Two positive integers as string, return their sum

JavaScript Math: Exercise-77 with Solution

Write a JavaScript program to compute the sum of two non-negative integers num1 and num2 represented by strings.

Test Data:
("123", "123") -> 246
("45", "100") -> 145

Sample Solution:

JavaScript Code:

/**
 * Function to perform addition of two large numbers represented as strings.
 * @param {string} n1 - The first number as a string.
 * @param {string} n2 - The second number as a string.
 * @returns {string} - The sum of the two numbers as a string.
 */
function test(n1, n2) {
    // Initialize an empty string to store the result
    var str = '';
    // Initialize the carry to 0
    var carry = 0;
    // Initialize the index for the first number
    var num1 = n1.length - 1;
    // Initialize the index for the second number
    var num2 = n2.length - 1;
    // Initialize a variable to store the sum of two digits
    var sum_of_two;

    // Loop until both numbers are exhausted
    while (num1 >= 0 || num2 >= 0) {
        // Calculate the sum of two digits from each number and add the carry
        sum_of_two = (parseInt(n1[num1]) || 0) + (parseInt(n2[num2]) || 0) 
        sum_of_two += carry ? 1 : 0;
        
        // If the sum is greater than 9, set the carry and append the unit digit to the result
        if (sum_of_two > 9) {
            carry = 1;
            str = sum_of_two % 10 + str;
        } else {
            // If the sum is less than or equal to 9, append the sum to the result
            str = sum_of_two + str;
            // Reset the carry to 0
            carry = 0;
        }
        // Move to the next digits of both numbers
        num1--;
        num2--;
    }
    // If there is still a carry after the loop, append it to the result
    if (carry) {
        str = 1 + str;
    }
    // Return the final result
    return str;
}

// Test cases
console.log(test("123", "123"));
console.log(test("45", "100"));

Output:

246
145

Flowchart:

Live Demo:

See the Pen javascript-math-exercise-77 by w3resource (@w3resource) on CodePen.

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