linking problem betn two C Files

[EMBEDED SOFTWARE FOR GUI OF A SPECTRUM A]

I face a linker problem in my program .Here I have 2 .C files betn these two one contains main() function . Now I call a user defined function from main () .The function body i.e definition is in second C file but declaration is in first .C file . During run time its giving "Multiply symbol

 _X in A.c and B.c ". Where X =Name of the user-defined function .

                                             A.c & B.c are two C Files .

Please reply whats wrong and how to recover from this problem ?

subrata

[RobertoBozzolo]

The problems you are seeing derive on the function being defined in both C files: the compiler detects this conditions and raises an error.
You must change the declaration in the source file with main () function to be a referencing declaration by adding the extern keyword.