C Exercises: Check if a given number is nearly prime or not

Last update on March 18 2025 13:28:16 (UTC/GMT +8 hours)

Check if a number is "nearly prime"

Write a C program to check if a given number is nearly prime number or not.
Nearly prime numbers are a positive integer which is equal to the product of two prime numbers

Sample Solution:

C Code:

#include <stdio.h>

// Define the number of primes to generate
#define NUM_OF_PRIMES 3500

// Function to check if a number is prime
int is_prime(int num);

int main() {
int primes[NUM_OF_PRIMES], num_of_primes = 0;    

    // Initialize the list of primes with the first prime number
primes[num_of_primes++] = 2;

    // Generate primes up to 1000000000
for(int num = 3; num * num<= 1000000000; num++) {
int flag = 1;

        // Check if num is divisible by any previously generated primes
for(int id = 0; id <num_of_primes; id++) {
if(num % primes[id] == 0) {
flag = 0;
break;
            }
        }

        // If num is prime, add it to the list of primes
if(flag) primes[num_of_primes++] = num;
    }

int N, num;
scanf("%d", &num);
int flag = 0;

    // Check if num is a Nearly prime number
for(int j = 0; (j <num_of_primes) && (primes[j] * primes[j] <= num); j++) {
if(num % primes[j] == 0) {
num /= primes[j];
flag = 1;
break;
        }
    }

    // Check if the remaining number after division is also prime
if(flag &&is_prime(num)) 
printf("It is a Nearly prime number.\n");
else
printf("It is not a Nearly prime number.\n");

return 0;
}

// Function to check if a number is prime
int is_prime(int num) {
if(num != 2 &&num % 2 == 0) 
return 0;

for(int factor = 3; factor * factor <= num ; factor += 2) {
if(num % factor == 0) 
return 0;
    }

return 1;
}

Sample Output:

It is not a Nearly prime number.

Flowchart:

For more Practice: Solve these Related Problems:

Write a C program to check if a number is nearly prime by verifying it is the product of exactly two distinct primes.
Write a C program to determine if a number qualifies as nearly prime using efficient prime factorization.
Write a C program to check nearly prime numbers and list their prime factors if the condition is met.
Write a C program to validate whether a number is nearly prime and output a message with its prime factors.

C programming Code Editor:

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