Question

In ASCII C programming write a function that determines if an integer is prime. A prime number is one
that is not divisible by any number other than one and itself.
int isPrime(long num);
Return 1 if num is prime, 0 if not. As above, make this a pure function contained in
its own file isPrime.c and test it with a separate tester program.
To test if an integer is prime you could implement a loop that generates trial divisors
from 2 to num-1. If any trial divides num, then num is not prime. But you only have to
test up to (and including) the integer square root of num. Say that num=a*b. Then if
a is larger than the square root, b must be smaller than the square root and has
already been tested.
Use your own function isqrt() for computing the integer square root. You will need
a prototype for this in isPrime.c
C:\Source\>gcc primeTester.c isqrt.c isPrime.c
C:\Source\>.\a.exe
Enter num: 223
223 is a prime

Answer 1

isPrime.c

#include <stdio.h>

#include <math.h>

int isPrime(long num) {

if (num <= 0)

return 0;

if (num == 2)

return 1;

if (num % 2 == 0)

return 0;

for (int i=3; i<sqrt(num); i+=2) {

if (num % i == 0) {

return 0;

}

}

return 1;

}

driver.c

#include <stdio.h>

#include <math.h>

#include "isPrime.c"

// driver code

int main() {

long num;

printf("Enter a number: ");

scanf("%ld", &num);

if (isPrime(num) == 1) {

printf("%ld is a prime.", num);

} else {

printf("%ld is not a prime.", num);

}

}

​​​​​​​

clang version 6.0.0-1ubuntu2 (tags/RELEASE_600/final) Enter a number: 223 223 is a prime.