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Program to find Prime Numbers Between given Interval

C Program To Check Prime Number By Creating a Function

Last Updated : 20 Aug, 2024

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Write a C program that checks whether a given number is a prime number by creating a dedicated function. A dedication function is better when we want to use the code multiple times in the program without making any changes.

Example:

Input: N = 7
Output: Prime
Explanation: 7 has no divisors other than 1 and 7, so it is a prime number.

Input: N = 10
Output: Not Prime
Explanation: 10 is divisible by 1, 2, 5, and 10, so it is not a prime number.

Different Methods to Check Prime Numbers Using Function in C

Table of Content

Using Function for Trial Division Approach
Using Function for Optimized Trial Division Approach

1. Using Function for Trial Division Approach

The idea of this approach is to check the divisibility of the number N with each number from 2 to N−1. If it is completely divisible by any number, then it is not a prime number.

Implementation

C

// C Program to Check Prime Number using Simple Trial // Division Approach #include <stdio.h>  int isPrime(int N) {        // Check divisibility from 2 to N-1     for (int i = 2; i < N; i++) {                // If N is divisible by i, it is not a prime number         if (N % i == 0) {             return 0;         }     }      // If no divisors were found, N is a prime number     return 1; }  int main() {     int N = 10;     printf("Is %d prime?\n", N);      // Check if the number is prime     if (isPrime(N)) {         printf("Yes\n");     }     else {         printf("No\n");     }      return 0; }

Output

Is 10 prime? No

Time Complexity: O(N)
Auxiliary Space: O(1)

2. Using Function for Optimized Trial Division Approach

In the above approach, we only need to check for factors up to the square root of N because if N is divisible by any number greater than its square root, then the quotient would be smaller than the square root and would have been checked already.

Implementation

C

// C Program to Check Prime Number using Square Root Optimized // Trial Division Approach #include <math.h> #include <stdio.h>  int isPrime(int N) {        // Check divisibility from 2 to sqrt(N)     for (int i = 2; i <= sqrt(N); i++) {                // If N is divisible by i, it is not a prime number         if (N % i == 0) {             return 0;         }     }        // If no divisors were found, N is a prime number     return 1; }  int main() {     int N = 10;   	printf("Is %d prime?\n", N);      // Check if the number is prime     if (isPrime(N)) {         printf("Yes\n");     }     else {         printf("No\n");     }      return 0; }

Output

Is 10 prime? No

Time Complexity: O(√N)
Auxiliary Space: O(1)

Related Articles:

Prime Numbers in C
Program to find Prime Numbers Between given Interval

Program to find Prime Numbers Between given Interval

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Article Tags :

C Language
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