BY TEJAS

In this example, we will check a number is a Prime Number or Not.

First we will see

**What is a Prime Number?
**

According to the mathematical definition of a prime number, "Prime number is a number which cannot be divided by the exactly whole number except itself and by the number 1".

For e.g. 5, 59, 97 are some prime numbers.

So let's take a turn to our example

In this example from the `scanf()`

function, we will get the number from the user which number we have to check is it a "prime number or not".

We will do this example by using "If.....Else" statement and "For..." statement.

This example is little-bit confusing example for begginers.

We use for statement `(i=2;i<=n/2;++i)`

Then we use "if....else" condition for a non-prime number.

You will get the idea when you see the program.

Note:- In Last of the Page there is a Program Code

Below video shows Working of Program

` ````
#include <stdio.h>
int main() {
int n, i, flag = 0;
printf("Enter a positive number: ");
scanf("%d", &n);
for (i = 2; i <= n / 2; ++i) {
// condition for non-prime numbers
if (n % i == 0) {
flag = 1;
break;
}
}
if (n == 1) {
printf("1 is neither prime nor composite.");
}
else {
if (flag == 0)
printf("%d is a prime number.", n);
else
printf("%d is not a prime number.", n);
}
return 0;
}
```

` ````
Enter a Positive Number: 5
5 is a prime number
```

` ````
#include <stdio.h>
int main() {
int n, i, flag = 0;
printf("Enter a positive number: ");
scanf("%d", &n);
for (i = 2; i <= n / 2; ++i) {
// condition for non-prime numbers
if (n % i == 0) {
flag = 1;
break;
}
}
if (n == 1) {
printf("1 is neither prime nor composite.");
}
else {
if (flag == 0)
printf("%d is a prime number.", n);
else
printf("%d is not a prime number.", n);
}
return 0;
}
```

` ````
Enter a Positive Number: 5
5 is a prime number
```