Prime Number Programs in C language

In this tutorial, we will learn how to check whether the given number is a prime number or not, and how to print all the prime number between two given numbers, using C programming language.

What is a Prime Number?

A prime number is a number that can be divided only by one and the number itself. The prime numbers from 1 to 100 are 2, 3, 5, 7, 11, 13, 17, 19, 23, 29,..., 89, and 97.

Note: 0 and 1 are not accepted as prime numbers. And 2 is the only even prime number in all prime numbers.

Program 1:

A C program that uses a “for” loop to check if a specified number is a prime number:

#include <stdio.h> 
int main() 
{
  int num, k, z = 0;
  printf("Enter a number : "); 
  //put a number which we want to check whether it is prime number or not


  scanf("%d", &num); 


  
  for (k = 2; k < num; k++) 
   {
      if (num % k == 0)
	   {
         z++;
         break;
       }
   }


  if (z == 1) {
        printf("It is not a Prime number");
  }
  else {
         printf("It is a Prime number");
  }
  return 0;    
}

Output: (When we put 5 as input)

It is a Prime number

Output: (When we put 10 as input)

It is not a Prime number

Description:

Given num = 5, any number should be considered.
Take some variables and use the printf() function.
Use the scanf() function to value from the user. This means that we want to know if the input is a prime number.
A prime number is a type of number that can only be divided by 1 and the number itself. Therefore, we need to run a for loop where the iterator starts at 2 and runs to (num-1). It is checked if num is divided by any number from 2 to (num-1).
When split, the code breaks out of the loop.
Then we need to check if the loop is running completely. When the loop is complete, it will be primed. Otherwise, it will be compound or non-prime.
The logic should be written as
for (i = 2; i 2; i <5; i ++). Here, the loop continues until the value of i equals 5.
Then we will use the `if` statement as well. If the condition is true, the "if" statement is executed.
Otherwise, the "else" part is executed.

Program 2:

A C program that uses a while loop to check if a specified number is a prime number:

#include<stdio.h>


int main()
{
	int n, p=0, z=2;


 	printf("Enter any number : ");
  //put a number which we want to check whether it is prime number or not


	scanf("%d", &n);


	while(z<n)


	{
	
		if(n%z==0){
		   p++;
		   break;
		}
		z++;
	}
	if(p>0)
		printf("It is not a prime number");
	else 
		printf("It is a prime number");
    return 0;


}

Output: (When we put 11 as input)

It is a Prime number

Output: (When we put 8 as input)

It is not a Prime number

Description:

If num = 8, we need to consider any number.
Take some variables and use the printf () function.
Here we use the scanf() function to get the input from the user. This means that we want to know if the input is a prime number.
A prime number is a type of number that can only be divided by 1 and the number itself. Therefore, we need to execute a while loop with the condition is running completely. When the loop is complete, it will be primed. Otherwise, it will be compound or non-prime.
The logic is written as while (z & lt; n). Here, the loop continues until the value of z equals 8.
Then we will use the `if` statement as well. If the condition is true, the "if" statement is executed.
Otherwise, the "else" part is executed.

Program 3:

C program to get the outputs of all prime numbers from 1 to 100:

#include <stdio.h>
int main()
{
  int q, p, c; 
  	printf("All the prime numbers from 1 to 100 are : ");


  for(p = 1; p <= 100; p++)
  {
    c = 0;
    for (q= 2; q <= p/2; q++)
    {
  	if(p%q== 0)
  	{
     	  c++;
  	  break;
	}
    }
    if(c == 0 && p!= 1 )
    {
	 printf(" %d ", p);
    }  
  }
  return 0;
}

Output:

All the prime numbers from 1 to 100 are :  2  3  5  7  11  13  17  19  23  29  31  37  41  43  47  53  59  61  67  71  73  79  83  89  97

Program 4:

C Program to print prime numbers between two given numbers:

#include <stdio.h>
int main() {
  int first , last, check;
   printf("Enter the two limits: ");
   scanf("%d %d", &first, &last);
   printf("The prime numbers which are in between of %d and %d are: ", first, last);


   // iteration will go on until first is not equal to last
   while (first < last) {
      check = 0;


      // ignore numbers less than 2
      if (first <= 1) {
         ++first;
         continue;
      }


      // if first is a non-prime number, check will be 1
      for (int j = 2; j <= first / 2; ++j) {


         if (first % j == 0) {
            check = 1;
            break;
         }
      }


      if (check == 0)
         printf("%d ", first);


      // to check the next number is prime or not
      // increase first by 1
      ++first;
   }
   return 0;
}

Output:

Enter the two limits: 5 15
The prime numbers which are in between of 5 and 15 are: 5 7 11 13

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