Question

write a function that will determine if an integer is prime. you should return 1 if the value is prime and 0 otherwise. you may not use the math library. create both function and prototype.

Answer 1

A number that is divisible only by 1 and itself is a prime number.
For example: 2, 3, 5, 7, 11, 13 etc.
Note: 1 is neither prime nor a composite number.

Below are the steps to check whether a number is prime or not a prime.
Step-1: Read the number and store it in the variable num.
Step-2:  Call the function primeNum, by passing the value. Check if the entered number is equal to 1(num==1), if so, print the statement it is neither prime nor composite. If the entered number is other than 1 use the for loop to check whether the number is divisible by other number beginning, from i=2 to num/2 (remember a number is prime if it is divisible by 1 and itself, so i=2). Now use the if statement to check whether the remainder is zero after dividing the number by i, if the remainder is 0, return 0 to main function and print the number is not prime, else return 1 and print the entered number is prime.

NoteL Please refer to the screenshot of the program for code indentation and explanation.

C program to check whether the entered number is prime or not.

#include<stdio.h>

int primeNum(int);
int main()

{  
int num, res;
printf("Enter a number to check whether it is prime or not: ");
scanf("%d",&num);   
res = primeNum(num);

if ( res == 1 )
printf(" %d is a prime number.", num);

else if(res==0)
printf("\n %d is not a prime number", num);
return 0;

}

/*Function to check whether a number is prime or not. If prime returns 1, else returns 0 */
int primeNum(int num)

{  
int i;    
if(num==1)
{
printf(" 1 is neither prime nor a composite number ");  
}
else  
{

for ( i = 2 ; i <= num/2 ; i++ )
{
  if ( num%i == 0 )

return 0;  
}
return 1;
}

}

The screenshot of the complete program along with the explanation and output is shown below:

8 1 #include<stdio.h> 2 3 //function declaration 4 int primeNum(int); 5 6 int main() 7-{ int num, res; // variable declaration 9 10 printf("Enter a number to check whether it is prime or not: "); 11 scanf("%d",&num); //read the entered number 12 13 primeNum(num); // calling the function primeNum 14 15 if ( res 1) //if the returned value i.e. result is equal to 1, then print prime number 16 printf(" %d is a prime number.", num); 17 else if(res==0)//if the returned value i.e. result is equal to 0, then print not a prime number 18 printf("\n %d is not a prime number", num); 19 20 return 0; 21 } res =

{ 22 //function definition 23 int primeNum(int num) 24 - { 25 int i; // variable declaration 26 27 if(num==1) // if entered number is 1, print the below statement 28 29 printf(" 1 is neither prime nor a composite number "); 30 } 31 else 32. 33 // begin checking whether the number is divisible by any other number from i=2 to num/2 for (i = 2; i <= num/2 ; i++) 35 - 36 //condition for a non prime number 37 if (numi = 0) 11 , if the number is divisible by other number i, return @ 38 return 0; 39 40 return 1; // if the number is prime, return 1. 41 } 42 } 43 { 34 { }
Output-1:

Enter a number to check whether it is prime or not: 3 prime number. 3 is a

Output-2:

Enter a number to check whether it is prime or not: 12 12 is not a prime number

Output-3:

Enter a number to check whether it is prime or not: 1 1 is neither prime nor a composite number