C Program To Check number is prime or not using loops

2. //C Program to Check a number whether it is prime or not using for loop
3. 
   
4. #include <stdio.h>
5. int main() {
6.     int number, i, a = 0;
7.     printf("Enter a positive Number To Check whether it is prime or not:- ");
8.     scanf("%d", &number);
9. 
   
10.  if(number<0)
11.     {
12.         printf("You Entered Negative Number , Please Enter Positive Number.");
13.         exit(0);
14.      }
15. 
    
16.     for (i = 2; i <= number / 2; ++i) {
17. 
    
18.         if (number % i == 0) {
19.             a = 1;
20.             break;
21.         }
22.     }
23. 
    
24.     if (number == 1) {
25.         printf("1 is neither prime number nor composite number.");
26.     }
27.     else {
28.         if (a == 0)
29.             printf("%d is a prime number.", number);
30.         else
31.             printf("%d is not a prime number.", number);
32.     }
33. 
    
34.     return 0;
35. }

Output

2. //C Program to Check a number whether it is prime or not using while loop
3. 
   
4. #include <stdio.h>
5. int main() {
6.     int number, i=2, a = 0;
7.     printf("Enter a positive Number To Check whether it is prime or not:- ");
8.     scanf("%d", &number);
9. 
   
10.  if(number<0)
11.     {
12.         printf("You Entered Negative Number , Please Enter Positive Number.");
13.         exit(0);
14.      }
15. 
    
16.     while (i <= number / 2 ) 
17. {
18.         if (number % i == 0) {
19.             a = 1;
20.             break;
21.         }
22.           i++;
23.     }
24. 
    
25.     if (number == 1) {
26.         printf("1 is neither prime number nor composite number.");
27.     }
28.     else {
29.         if (a == 0)
30.             printf("%d is a prime number.", number);
31.         else
32.             printf("%d is not a prime number.", number);
33.     }
34. 
    
35.     return 0;
36. }

Output

1. 
   
2. //C Program to Check a number whether it is prime or not using do-while loop
3. 
   
4. #include <stdio.h>
5. int main() {
6.     int number, i=2, a = 0;
7.     printf("Enter a positive Number To Check whether it is prime or not:- ");
8.     scanf("%d", &number);
9. 
   
10.  if(number<0)
11.     {
12.         printf("You Entered Negative Number , Please Enter Positive Number.");
13.         exit(0);
14.      }
15. 
    
16.     do
17. {
18.         if (number % i == 0) {
19.             a = 1;
20.             break;
21.         }
22.           i++;
23.     }while (i <= number / 2 ) ;
24. 
    
25.     if (number == 1) {
26.         printf("1 is neither prime number nor composite number.");
27.     }
28.     else {
29.         if (a == 0)
30.             printf("%d is a prime number.", number);
31.         else
32.             printf("%d is not a prime number.", number);
33.     }
34. 
    
35.     return 0;
36. }

Output