C programming using linux terminal

[sudeep93]

Whenever i run this code(on linux terminal):

#include <stdio.h>
#include <math.h>
int main()
{
double x,y;
printf ("enter the angle between the two sides(in radians): \n");
scanf ("%lf",&x);
y= cos(x);
printf ("the cosine of the angle is: %lf\n",y);
return 0;
}

I always get this error:

/tmp/cckIyjg6.o: In function `main':
CosineRule.c:(.text+0x33): undefined reference to `cos'
collect2: ld returned 1 exit status

whats the problem with my code? please help..

[weaknessforcats]

There are no errors in the code you posted.

The error is in CosineRule.c. Did you include <math.h> in that file?

[Luuk]

@weaknessforcat s: it is there at line 2 ...

i googled and found this:
use: cc CosineRule.c -o CosineRule -lm
(http://www.cs.cf.ac.uk/Dave/C/node17.html)

[donbock]

When you include <math.h> it is a little bit like telling the compiler: "Yes, I know these functions (such as cos) are not in my source file; but trust me, you'll have them when you need them."
That error message is the compiler's way of saying: "You let me down -- I didn't have this function when I needed it."
The -lm command line argument to the compiler directs it to look in library m (file libm.a) for anything that it still needs. As it happens, libm is where the <math.h> functions are kept (m is for math) so now the compiler is happy because it has everything it needs.

You might ask: "Why isn't libm automatically included?" The simple answer is that the C Standard does not require that behavior. The real answer is that C allows you the leeway to write your own cos function -- and you can even go so far as to write a cos function that has nothing to do cosines. I'm not suggesting it would be wise to do this, but it is allowed.