C Exercises: Check whether a number is a prime number or not

C Function : Exercise-7 with Solution

Write a program in C to check whether a number is a prime number or not using the function.

Pictorial Presentation:

Sample Solution:

C Code:

#include<stdio.h>
int PrimeOrNot(int);
int main()
{
    int n1,prime;
	printf("\n\n Function : check whether a number is prime number or not :\n");
	printf("---------------------------------------------------------------\n");    	

    printf(" Input a positive number : ");
    scanf("%d",&n1);
    prime = PrimeOrNot(n1);
   if(prime==1)
        printf(" The number %d is a prime number.\n",n1);
   else
      printf(" The number %d is not a prime number.\n",n1);
   return 0;
}
int PrimeOrNot(int n1)
{
    int i=2;
    while(i<=n1/2)
    {
         if(n1%i==0)
             return 0;
         else
             i++;
    }
    return 1;
}

Sample Output:

 Function : check whether a number is prime number or not :
---------------------------------------------------------------
 Input a positive number : 5
 The number 5 is a prime number.

Explanation:

int PrimeOrNot(int n1) {
  int i = 2;
  while (i <= n1 / 2) {
    if (n1 % i == 0)
      return 0;
    else
      i++;
  }
  return 1;
}

The function 'PrimeOrNot' takes a single argument 'n1' of type int. It checks whether the input number 'n1' is prime or not by iterating through all integers from 2 to n1/2. The function initializes a local integer variable i to 2 and enters a while loop that continues as long as i is less than or equal to n1/2. In each iteration of the loop, the function checks if 'n1' is divisible by i. If it is, the function returns 0, indicating that n1 is not a prime number. Otherwise, i is incremented by 1 and the loop continues. If the loop completes without finding any divisors of 'n1', the function returns 1, indicating that n1 is a prime number.

Time complexity and space complexity:

The time complexity of this function is O(n), where n is the input number n1, because the while loop iterates n1/2 - 2 + 1 times.

The space complexity of this function is O(1), as it only uses a fixed amount of memory to store the single integer variable i.

Flowchart:

C Programming Code Editor:

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