# Learn how to check a number is prime or not in C langage In this article, you’ll learn how to check a given number is prime or not in C language without giving input from the keyboard or giving input from the keyboard.

Q: what is a prime number

Ans: A natural number which only divided by itself and 1 is called a prime number and you also say that a prime number is a natural number which is greater than 1 and cannot be formed by multiplying two natural number.

• 1 is not a prime number.
• 2 is the smallest prime number and only even prime number.
• Example of prime number 2,3,5,7,11,13 etc.

#### To check a given number is prime or not we generally use the following steps:

• Let the given number be x.
• Then we create a loop for checking the given number is prime or not.
• Loop i=2 to x-1, we start the loop at 2 and check up to the given number – 1. Here i is a variable and its initial value is 2, check up to i=x-1.
• If (x % i==0) is false then the given number is prime otherwise it is not prime.

#### Loop is terminated two times:

• First time, when the condition is true, terminated from the loop and with the help break keyword print on the screen number is not prime.
• Second time, when the condition is false ( it means when the loop is fully executed) and print on the screen number is prime
• If (i==x) is true then the number is prime
• Else
• The number is not prime.

Example 1: write a program in C language to check whether a number is prime or not, without input from keyboard

 #include #include int main() {   int x=17,i;   for(i=2;i<=x;i++)   if(x%i==0)   break;   if (i==x)   printf(“%d is a prime number”,x);   else   printf(“%d is not a prime number”,x);   getch(); }

 The Output of this program: 17 is a prime number 