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In this C program, we are going to learn to **check prime numbers in an array**. We will declare an array with some prime and non prime numbers, and then print the elements with 'prime' and 'Not prime' message.

Submitted by **IncludeHelp**, on March 09, 2018

**Given an array of integer elements and we have to check which prime numbers using C program are.**

**Example:**

Input: Array elements are: 100, 200, 31, 13, 97, 10, 20, 11 Output: 100 - Not Prime 200 - Not Prime 31 - Prime 13 - Prime 97 - Prime 10 - Not Prime 20 - Not Prime 11 - Prime

**Logic:**

- We are declaring an array (arr) with the elements: 100, 200, 31, 13, 97, 10, 20, 11
- To check prime numbers, we declare a function isPrime() that will return 1, if number is prime and return 0 if number is not prime.
- Then, in main() function - we are using a loop with 0 to len-1 (total number of array elements) and calling isPrime() by passing array elements one by one (arr[loop]) – Here, loop is a loop counter.
- Then we are checking a condition with print statement: (isPrime(arr[loop])?"Prime":"Not Prime") - This will return/print
**"Prime"**, if isPrime(arr[loop]) will return 1 or this will return/print**"Not Prime"**, if isPrime(arr[loop]) will return 0.

#include <stdio.h> //function to check number is prime or not //function will return 1 if number is prime int isPrime(int num) { int i; //loop counter //it will be 1 when number is not prime int flag=0; //loop to check number is prime or not //we will check, if number is divisible //by any number from 2 to num/2, then it //will not be prime for(i=2; i<num/2; i++) { if(num%i ==0) { flag =1; break; } } //flag is 1, if number is not prime if(flag==1) return 0; else return 1; } int main() { int loop; //loop counter //declaring array with prime and not prime numbers int arr[]={100, 200, 31, 13, 97, 10, 20, 11}; //calculate length of the array int len = sizeof(arr)/sizeof(arr[0]); //print array elements with message //"prime" or "Not prime" for(loop=0; loop<len; loop++) { printf("%3d - %s\n",arr[loop],(isPrime(arr[loop])?"Prime":"Not Prime")); } printf("\n"); return 0; }

**Output**

100 - Not Prime 200 - Not Prime 31 - Prime 13 - Prime 97 - Prime 10 - Not Prime 20 - Not Prime 11 - Prime

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