LinkerError- unresolved external symbol

[RajaKavi]

Hi,
When i tried to call a function, i received a linker error Unresolved external symbol.

Example:

sample.h

void add(int x, int y) ;
void sub(int a, int y);
.
.
.

sample.c

.
.
.
c = add(a,b);
d = sub(a,b);
.
.
.
Note:
Like this i used to develop my application, i included some 10 to 20 functions, and i dont have any problem with most of the function call except for only one function i have error ( for example in my above snip the add(a,b) function works fine but sub(a,b) shows linker error).

I also checked, this two functions were defined or not. I found the definition was provided for all the functions. Please help me.

Thanks
V.Raja