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Problem with math.h

I should be bashed to death for not being able to do this :) ...I just started learning C, I am using gcc 3.2.3 on a linux box. This is the code I wrote, which finds prime numbers below 100:

Code:

#include <stdio.h>

#include <math.h>





main ()

{

int i, j;

printf ("%d\n", 2);



for (i=3; i<100; i=i+1)

        {

        for (j=2; j<i;j=j+1)

                {

                if (i%j ==0)

                        break;

                if (j > sqrt(i))

                        {

                        printf ("%d\n");

                        break;

                        }

                }

        }

return 0;

}

And this is the error msg I get after attempting to compile:

Code:

bash-2.05b$ gcc primo.c -o primo

/tmp/ccZdYpje.o(.text+0x65): In function `main':

: undefined reference to `sqrt'

collect2: ld returned 1 exit status

bash-2.05b$

Isn`t sqrt defined in math.h??

Thanks

Use gcc -lm -o myprog myprog.c

The "-lm" invokes linking of the math library.

Re: Problem with math.h

Quote:

Originally posted by loke137
Isn`t sqrt defined in math.h??

Well, yes, it is. But in case of the math library, you also need to link with the math library. It's very understandable that you, as a beginner, didn't know this as for most standard things you #include there's no need for linking with seperate libraries.

Assuming you c-file is called "prime.c", and you want the executable be called "prime", compile with this command line

Code:

gcc -lm -o prime prime.c

"-lm" makes sure the math library is linked.

You'll also see another error, because you forgot to pass the variable i to the printf statement. Change the line to:

Code:

printf ("%d\n", i);

Also, it's better to declare main() as "int main()". If you don't specify "int" as the return type of main(), you'll get a warning. Not a big deal though, it's only warning, not an error.

Compile with this to make the compiler report all possible warnings:

Code:

gcc -Wall -pedantic -lm -o prime prime.c

Thank you...so it was a problem about compiler knowledge :)

To be pedantically precise: it was a problem about linking knowledge :-)