Question

In my homework for my C class, we have to write a program that checks if an integer is prime. I am getting an error at the sqrt() function. My professor told me that num must be an integer and we must use the sqrt() function. I thought the problem was that the sqrt() function can’t be used on an integer but my professor told me that it can, and that I was getting an error from something else. Do you guys see the problem?

int primality(int num)
{

int isprime;

    /*check if num is prime*/
    for (int i = 2; i <= sqrt(num); i++)
    {
        if (num % i == 0)
            isprime = 0; /*is not prime*/
        else 
            isprime = 1; /*is prime*/
    }

    if (isprime == 0)
        return 0;
    elseif (isprime == 1)
        return 1;
}

EDIT:
Yes I am using math.h and compiling as C code.

The error msg is “Error: More than one instance of overloaded function “sqrt” matches the argument list.

Answer 1

The C language does not have “overloads”. My bet is that you are compiling your code as C++, not C. If you’re using GCC, compile with gcc, not g++. If you are using Visual Studio, there is an option in the properties of the project:

1. right click on your project
2. click properties
3. click on C/C++
4. click on advanced
5. set the property “compile as” to C Code (/TC)

In either case, name your file with a .c extension (lowercase ‘c’).

Indeed, in C there is only one sqrt, defined as

double sqrt(double);

and integers convert to double.