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Prime Number code in C

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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