# C program to check prime numbers in an array

C program to check prime numbers in an array

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## Code Explanation :

In this example, we are going to learn to prime number in array. We have declared an array with certain prime and non-prime numbers, then print the elements with the message 'prime' and 'Not prime'.

We have to check whether number is prime or not from given single dimension array.

Example:

```    Input:
Array elements are:
120, 200, 35, 13, 7, 10, 3, 90

Output:
120 - Not Prime
200 - Not Prime
35 - Not Prime
13 - Prime
7 - Prime
10 - Not Prime
3 - Prime
90 - Not Prime
```

Logic:

• We have declared an array (arr) with the elements: 120, 200, 35, 13, 7, 10, 3, 90
• To test the prime numbers, we declare an ` isPrime() `function returning 1, if number is prime and returning 0 if number is not prime.
• Then we have used a loop with 0 to len-1 (total number of array elements) and call `isPrime() `by moving array elements one by one (`arr[loop]`) in `main()` function.
• Then we check a print statement condition: `(isPrime(arr[loop])?"Prime":"Not Prime"))`. This return "Prime", if `isPrime(arr[loop])` returns 1 and return "Not Prime", if `isPrime(arr[loop])` returns 0.

This is the main concept of this program.

If you want to do smae problem without using function then it is very easy.

```#include <stdio.h>
int isPrime(int);

int main()
{
int loop, i, flag; //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);

//print array elements with message
//"prime" or "Not prime"
for(loop=0; loop < len; loop++)
{
flag = 0;
for(i=2; i < arr[loop] / 2; i++)
{
if(arr[loop] % i ==0)
{
flag = 1;
break;
}
}
//flag is 1, if number is not prime
if(flag == 1){
printf("%3d - Not Primen",arr[loop]);
}
else
{
printf("%3d - Primen",arr[loop]);
}
}

printf("n");

return 0;
}```

The algorithm and flowchart of this progrem is:

## Algorithm

```STEP 1 : Start;

STEP 2 : Declare variable arr[], loop, i and flag;

STEP 3 : Initialize arr[] = {100, 200, 31, 13, 97, 10, 20, 11};

STEP 4 : Get the length of array;

STEP 4 : Repeat this process until loop < len
STEP 4.1 : flag = 0
STEP 4.2 : Repeat this process until i < arr[loop]
STEP 4.2.1 : flag = 1
STEP 4.2.2 : break
STEP 4.3 : IF flag == 1 THEN
Print prime
ELSE
Print not prime
STEP 4.4 : loop++

STEP 5 : End```

## Flowchart If you got any problem on understanding this example then please comment below.

Our example mainly covers following topics in any programing

• Basic Programs
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• Array Programs
• Matrix Programs
• Pattern Programs
• String Programs
• Tree Programs

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