Calling function from another file declared in a header file

Question

I want to call a function that is in sin.c, and the main file is in test1.c

and the files look like this:

file test1.c:

    #include <stdio.h>
    #include <stdlib.h>
    #include "sin.h"

    int main(){
       float angle;
       double sinValue;

       printf("Please enter a angle: ");
       scanf("%f", &angle);

       sinValue = sin(angle);

       printf("the sin value of this angle is: %2.7f.", sinValue);
       printf("program terminated");

       return 0;
    }

this is the header file:

In sin.h:

extern double sin(float angle);

In file sin.c:

#include <math.h>
#include <stdlib.h>
#define EPSILON 0.0000001;

int fact(int n);

double sin(float angle){

    float rad;
    float pi = M_PI;
    double newSin, oldSin;
    double n = 1.0;
    double token;


    //find the radians
    rad = angle * M_PI / 180.0;
    newSin = rad;

    //find the approxmate value of sin(x)
    while((newSin - oldSin) > EPSILON ){

        oldSin = newSin;
        token = 2.0 * n - 1.0;
        newSin = oldSin + pow(-1.0, n) * pow(rad, token) / fact(token);
        n++;
    }

    return newSin;
}

The problem is when I compile the test1.c the error message shows:

sin.h:1:15: warning: conflicting types for built-in function ‘sin’      [enabled by default]
 extern double sin(float angle);
               ^
/tmp/ccxzixfm.o: In function `main':
test1.c:(.text+0x39): undefined reference to `sin'
collect2: error: ld returned 1 exit status
make: *** [test1] Error 1

It is already declared in the header file and I also included that header file, so what is the error. I'm so confused.

Thanks before, John.

I use the "make" command to compile the test1.c

Here is the compilation process:

zxz111@ubuntu:~/Desktop/sin$ ls
sin.c  sin.c~  sin.h  test1.c  test1.c~
zxz111@ubuntu:~/Desktop/sin$ make test1
cc     test1.c   -o test1
In file included from test1.c:3:0:
sin.h:1:15: warning: conflicting types for built-in function ‘sin’ [enabled by default]
 extern double sin(float angle);
               ^
/tmp/ccxzixfm.o: In function `main':
test1.c:(.text+0x39): undefined reference to `sin'
collect2: error: ld returned 1 exit status
make: *** [test1] Error 1
zxz111@ubuntu:~/Desktop/sin$ make test1

Answer 1

You need to pass both source files to the compiler.

If you're using GCC it would be:

gcc sin.c main.c -o main

Although your fact() function doesn't seem to be defined anywhere and a function named sin() is already defined in <math.h> you probably wanna rename yours.