Looping Programs

1) Prime Number
i)Finding whether the given number is prime or not:

let num = 7;
let isPrime = true;

for (let i = 2; i < num; i++) {
    if (num % i === 0) {
        isPrime = false;
        break;
    }
}

if (num > 1 && isPrime) {
    console.log("Prime");
} else {
    console.log("Not Prime");
}

Output:

Prime

ii)Printing all the prime numbers within the 2-50:

for (let num = 2; num <= 50; num++) {

    let isPrime = true;

    for (let i = 2; i < num; i++) {
        if (num % i === 0) {
            isPrime = false;
            break;
        }
    }

    if (isPrime) {
        console.log(num);
    }
}

Output:

2
3
5
7
11
13
17
19
23
29
31
37
41
43
47

2) Reverse Printing a Number

        let num=1234;
        let reverse=0;
        while(num>0){
            let digit=num%10;
            reverse=reverse*10+digit;
            num=Math.floor(num/10);
        }
        document.write("Reverse: "+reverse);

Output:

Reverse: 4321

3) Count of Digits

        let num=1234;
        let count=0;
        while(num>0){
            let digit=num%10;
            num=Math.floor(num/10);
            count++;
        }
        document.write("Count of digits: "+count);

Output:

Count of digits: 4

4) Sum of Digits

let num = 123;
let sum = 0;

while (num > 0) {
    let digit = num % 10;
    sum += digit;
    num = Math.floor(num / 10);
}

console.log("Sum:", sum);

Output:

6

5) Palindrome

let num = 121;
let temp = num;
let reverse = 0;

while (num > 0) {
    let digit = num % 10;
    reverse = reverse * 10 + digit;
    num = Math.floor(num / 10);
}

if (temp === reverse) {
    console.log("Palindrome");
} else {
    console.log("Not Palindrome");
}

Output:

Palindrome

6) Swapping two numbers

let a = 5;
let b = 10;

let temp = a;  // store a
a = b;         // assign b to a
b = temp;      // assign temp to b

console.log("a =", a);
console.log("b =", b);

Output:

a = 10
b = 5

7) Swapping without third variable

let a = 5;
let b = 10;

a = a + b; // 15
b = a - b; // 5
a = a - b; // 10

console.log("a =", a);
console.log("b =", b);

Output:

a = 10
b = 5