sqrt() what am I doing wrong?

[Scribbler]

I'm getting this error message from gcc when trying to compile my code...

# gcc project7.c
/tmp/cc4pGFvN.o(.text+0xbb): In function `isPrime':
: undefined reference to `sqrt'
collect2: ld returned 1 exit status

I can't find anything wrong with the source...at least nothing obvious.
It doesn't seem to like the sqrt() function, yet as you can see I've included the math.h library.

#include <stdio.h>
#include <math.h>

int isPrime ( int number );

int main()
{
	int primeFound = 0;
	int number;
	
	for ( number = 3 ; number <= 10000 ; number += 2 )
	{
		if ( isPrime ( number ) )
		{
			primeFound++;
			printf ("%7d" , number);
			if ( primeFound % 5 == 0 )
				printf("\n");
			
		}
	}
	
	printf ("\nPrimes found %d\n" , primeFound);
	return 0;
}

int isPrime ( int number )
{
	int n;
	
	for ( n = 3 ; n <= sqrt(number) ; n += 2 )
	{
		if ( number % n == 0 )
			return 0;
	}
	
	return 1;
}

[bithub]

Link to the math library by passing -lm to the linker.
gcc -lm project7.c

[Salem]

And if that doesn't work, try a different order
gcc project7.c -lm

The position and order of libraries is important.

[Scribbler]

Doh! Thanks for the advice, but I found using g++ instead of gcc fixes the problem.

[itsme86]

Doh! Thanks for the advice, but I found using g++ instead of gcc fixes the problem.

Using g++ as a workaround is a poor solution to the problem. It can lead to weird thing happening in your programs or produce incorrect warning/error messages. You should use gcc to compile C programs and g++ to compile C++ programs.

Adding -lm to the compile command is the correct way to fix your problem.