In this post of C programming language for prime number program in c language, we will create C programs to print (find) prime numbers in different ways.

As you know, Prime Numbers are those whole numbers which are not divisible by only the number 1 and any other number other than itself.

In other words, prime numbers are said to be those numbers in which if you divide the number 1 and itself by any number other than that number, then the remainder (remainder) does not come to 0.

Prime Numbers Example:

2, 3, 5, 7, 11, 13, 17, 19

Apart from this, those numbers which are divisible by number 1 and other numbers other than ourselves, we call them composite numbers but number 1 is neither prime number nor composite number.

You can make a program to find or print prime numbers in C programming in many ways and therefore we will also make C programs to print prime numbers by taking number input from the user in the 4 ways given below.

To understand all the programs given in this tutorial, you must first be aware of for loop, functions and recursion.

## What is the logic of Prime Number Check?

Native Approach means a simple and common way of doing something. Let us now understand how we will find prime number.

As I mentioned above, Prime Numbers are those whole numbers which are not divisible by only the number 1 and any other number other than itself.

Therefore, in the number you want to check whether it is a prime number or not, except the number 1 and that number itself, all the numbers from number 2 to the half number (N/2) of that N number are one by one. By dividing.

We divide the number N only up to its half number (n/2) because the largest number that can divide any N number is the half number of that N number.

If the number N becomes completely divisible by any number, then it means that the number N is not a prime number. Let us understand this logic as the form of programs.

## You can also read: Data Types in C Programming

## Prime Number Program in C using for loop

In this program, we will take a number input from the user and then check and print whether that number is prime number or not.

```
#include<stdio.h>
int main()
{
int i,n,flag=0;
printf("Enter a number : ");
scanf("%d",&n);
for(i=2;i<=n/2;i++)
{
if(n%i==0)
{
flag=1;
break;
}
}
if(flag==0)
{
printf("%d is a prime number",n);
}
else
{
printf("%d is not a prime number",n);
}
return 0;
}
```

**Prime Number Program in C Language**

## Output 1:

Enter a number : 12 12 is not a prime number

## Output 2:

Enter a Number : 7 7 is a prime number

## Explanation:

We have initialized the value of variable flag above to 0 and if any value of variable i inside the loop divides the value of variable n then the value of variable flag will change.

If the value of the variable flag changes, it means that the variable n is divisible by number 1 and any number other than itself.

Note:

You can keep the name of the variable in place of the flag.

## C Program to Print all Prime Numbers from 2 to N

In this program, we will input a number in variable n from the user and then find and print all prime numbers from number 2 to variable n.

```
#include<stdio.h>
int main()
{
int i,j,n,flag;
printf("Enter a number : ");
scanf("%d",&n);
printf("All prime numbers from 2 to %d : ",n);
for(i=2;i<=n;i++)
{
flag=0;
for(j=2;j<=i/2;j++)
{
if(i%j==0)
{
flag=1;
break;
}
}
if(flag==0)
{
printf("%d ",i);
}
}
return 0;
}
```

**Prime Number Program in C Language**

## Output:

Enter a number : 18 All prime numbers from 2 to 18 : 2 3 5 7 11 13 17

## Prime Number Program in C using Function

```
#include<stdio.h>
int isPrime(int t);
int main()
{
int n,p;
printf("Enter a number : ");
scanf("%d",&n);
p=isPrime(n);
if(p==1)
{
printf("%d is a prime number",n);
}
else
{
printf("%d is not a prime number",n);
}
return 0;
}
int isPrime(int t)
{
int i;
for(i=2;i<=t/2;i++)
{
if(t%i==0)
{
return 0;
}
}
return 1;
}
```

**Prime Number Program in C Language**

## Output 1:

Enter a number : 12 12 is not a prime number

## Output 2:

Enter a Number : 7 7 is a prime number

## Prime Number Program in C using Recursion

```
#include<stdio.h>
int isPrime(int t,int i);
int main()
{
int n,p;
printf("Enter a number : ");
scanf("%d",&n);
p=isPrime(n,n/2);
if(p==1)
{
printf("%d is a prime number",n);
}
else
{
printf("%d is not a prime number",n);
}
return 0;
}
int isPrime(int t,int i)
{
if(i==1)
{
return 1;
}
else if(t%i==0)
{
return 0;
}
else
{
return isPrime(t,i-1);
}
}
```

**Prime Number Program in C Language**

## Output 1:

Enter a number : 12 12 is not a prime number

## Output 2:

Enter a Number : 7 7 is a prime number

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