Need second opinion on this error code

OpenGL OpenGL: Basic Coding
1

I am getting complains from Linux GCC about this basic (sample) code - implementation of “circle”.

Obviously something basic is wrong in my usage of sin/ cos.
BUT I do not see it.

What “reference” is missing ? “math” library??

Any help woudl be appreciated and I am sorry for such stupid math question / problem.

Linux GCC linker output

Building target: A_OPEGL_TUT_1
Invoking: GCC C Linker
gcc  -o "A_OPEGL_TUT_1"  ./src/A_OPEGL_TUT_1.o   -lglut -lGL -lGLU
/usr/bin/ld: ./src/A_OPEGL_TUT_1.o: undefined reference to symbol 'sin@@GLIBC_2.2.5'
makefile:30: recipe for target 'A_OPEGL_TUT_1' failed
//lib/x86_64-linux-gnu/libm.so.6: error adding symbols: DSO missing from command line
collect2: error: ld returned 1 exit status

Here is the code

    GLfloat GL_PI = PI;
	glColor3f(1.0f, 1.0f, 1.0f); // white
	float width = glutGet(GLUT_WINDOW_WIDTH);
	float height = glutGet(GLUT_WINDOW_HEIGHT);

	GLfloat x, y, angle,x_offset,y_offset,radius;
	//float size = 10;
	glColor3f(1, 0, 0);  // red 
	//float size = 25.0;
	glPointSize(size);
	glBegin( GL_POINTS);
	for (angle = 0.0f; angle <= (2.0f * GL_PI); angle += 0.01f) {
		x = radius * sin(angle);
		y = radius * cos(angle);
		//	glVertex3f(x, y, 0.0f);
		//printf(" x %f  y %f \n", x, y);
		glVertex2f(x +x_offset, y+y_offset);	//  0.0f);
		printf(" x %f  y %f \n", x, y);
		//printf(" window width  %f  window height  %f \n", width, height);
//#endif		//sleep(5);
	}
	glEnd();

	glFlush();
2

You need “-lm” for math functions such as sin.

3

Thanks.
This is a basic tutorial where I added “circle” to do some quick testing.
That’s odd, my main program does not have “m” library and “circle” works there. Since liker does not report “lm” it must be part of some other library.