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I have the code below:

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

int main(int argc, char **argv){

float index;
	for(index = 0; index <= 360; index++){
		index = (3.14/180) * index; //convert to radiant
		float a = cos(index);
		printf("a = %f\n", a);

And when I tried to compile, I got the error below:

/tmp/ccEPoXwg.o: In function `main':
test.c:(.text+0x6b): undefined reference to `cos'
collect2: ld returned 1 exit status

What is weird is that when I try this (without the for loop) :
float a = cos(3.14);
  printf("a = %f\n", a);

I get no errors

Can anyone, please help me.

Thank you in advance
Updated 19-Dec-10 5:52am

The problem is that you have only a cos(double) function in your math library but you are trying to call a cos(float) function in the loop. Without the loop you pass a double type number to cos() (because you say cos(3.14) and not cos(3.14f)). But in the loop you pass in a float (float index). Declare index as a double or cast index to a double when you call cos()!

Most math libraries contain a cos(double) and a cosf(float) function. You can try using cosf() if you want to stick with your float data!
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Richard MacCutchan 19-Dec-10 15:54pm    
Excellent answer, I certainly missed that subtle difference.
The_Real_Chubaka 20-Dec-10 4:57am    
Thank you for you answer. The main mistake i made is that i forgot to link with the math library. I also did not know that there was no cos(float) function in the math library. Thank you for that information too.
You must link with the math library, namely:
gcc myprogram.c -lm

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The_Real_Chubaka 20-Dec-10 4:59am    
Thank you. I did what you suggested.
My code works now.
Lightning Monster 18-Dec-22 15:11pm    
WTF My library is not working and I am finding a solution for this error for a week its solution is only type -lm when compiling!! BTW Thank U sir/madam!!
Check your build statement, or make script, to ensure that you are including the correct math library in your link phase.

pasztorpisti has the correct answer; well done considering the sample does not use Hungarian notation. :laugh:
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The_Real_Chubaka 20-Dec-10 4:58am    
Thank you for you answer. The code work now.
I just forgot to link with the math library.

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