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# Prime Number Or Not

## Prime number or not:-

Prime number program in C programming is to test whether the inserted number by the user is prime or not. A prime number is a natural number that is divisible by just 1 and itself. In order to test whether the number inserted by the user is prime or not, the C program runs an if-else statement for the same.

## Algorithm to check whether the inserted number is prime or not:

Step 1: Start

Step 2: The user is asked to enter a number

Step 3: Check whether the number is divisible by the natural numbers starting from 2.

Step 4: If the number is divisible, then it is not a prime number, if it is not, printf “the number is prime”.

Step 5: Exit

Read Also: Program for Prime Number in a given Range

### Program to check whether the inserted number is prime or not:

```/*
* C program to check whether a given number is prime or not
* and output the inserted digit with appropriate message.
*/
#include <stdio.h>
#include <stdlib.h>
void main()
{
int no, j, flag;
printf("Insert a no \n");
scanf("%d", &no);
if (num <= 1)
{
printf("%d is not a prime numbers \n", no);
exit(1);
}
flag = 0;
for (j = 2; j <= no / 2; j++)
{
if ((no % j) == 0)
{
flag = 1;
break;
}
}
if (flag == 0)
printf("%d is a prime num \n", no);
else
printf("%d is not a prime num \n", no);
}```

### Output

```Insert a no: 23
23 is a prime num
Insert a no. 15
15 is not a prime num```