prime number

Source: Dev.to

The Logic Building (The Strategy)

The general rule for a prime number is that it’s only divisible by 1 and itself. However, a common confusion is that composite numbers (like 4) are also divisible by 1 and themselves.

• Prime Number (e.g., 5): When divided by every number from 1 to itself, it produces a remainder of zero exactly two times ( 1 and 5 ).
• Composite Number (e.g., 4): It produces a remainder of zero more than two times ( 1, 2, and 4 ).

Recipe Writing (The Algorithm)

Treat the code like a recipe:

1. Input: Get the number.
2. Loop: Check every number from 1 up to the input number.
3. Check Remainder: Use the modulo operation (%) to find where the remainder is 0.
4. Counter: Count how many times the remainder was 0.
5. Final Result: If the count is exactly 2, it’s prime; otherwise, it’s composite.

The Ingredients (The Variables)

• input: The number to check.
• count: To track the number of divisors.
• for loop:
  • Start: 1 (initialization)
  • End: Input (condition)
  • Next step: +1 (increment)
• if‑else: To handle the logic.

Program (JavaScript)

var a = 24;
var c = 0;

for (i = 1; i <= a; i++) {
    if (a % i == 0) {
        c++;
    }
}

if (c == 2) {
    console.log("Prime");
} else {
    console.log("Not Prime");
}