Check if Number is Prime in DSA C - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if a number is less than 2, which is not prime.

DSA C

if (num [1] 2) {
    printf("Not prime\n");
    return 0;
}

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A>

B<

C==

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' instead of '<' to check for non-prime numbers.

Checking if num is greater than 2 here.

Numbers less than 2 are not prime, so we check if num is less than 2.

2fill in blank

medium

Complete the for loop to check divisors from 2 up to the square root of num.

DSA C

for (int i = 2; i [1] num / i; i++) {
    if (num % i == 0) {
        printf("Not prime\n");
        return 0;
    }
}

Drag options to blanks, or click blank then click option'

A<=

B<

C>

D>=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>' or '>=' which causes the loop to not run correctly.

Using '<' which can cause off-by-one errors in some cases.

The loop runs while i is less than or equal to the square root of num, so i <= num / i. The condition uses '<=' to continue looping.

3fill in blank

hard

Fix the error in the if condition to correctly check if num is divisible by i.

DSA C

if (num [1] i == 0) {
    printf("Not prime\n");
    return 0;
}

Drag options to blanks, or click blank then click option'

A%

B/

C*

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using '/' instead of '%' which performs division, not remainder check.

Using '*' or '-' which are incorrect operators here.

The modulus operator '%' checks if num is divisible by i with no remainder.

4fill in blank

hard

Fill both blanks to complete the function header and return type for checking prime.

DSA C

[1] is_prime(int num) {
    if (num < 2) {
        return [2];
    }
    // rest of code
}

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Aint

B0

Cvoid

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'void' as return type which cannot return a value.

Returning 1 for numbers less than 2 which is incorrect.

The function returns an int indicating true (1) or false (0). If num is less than 2, it returns 0 (not prime).

5fill in blank

hard

Fill all three blanks to complete the return statement that confirms the number is prime.

DSA C

return [1];

// Usage example:
// if (is_prime([2])) {
//     printf("%d is prime\n", [3]);
// }

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A1

Bnum

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Returning 0 which means not prime.

Using wrong variable names in usage example.

Return 1 to indicate prime. Use 'num' in the usage example to check and print the number.