C/C++ :: How To Remove Linker Error In CPP Programs With A Class

how to remove the linker error as mentioned above..

i have created a simple program in C++ as given below

#include<iostream.h>
#include<conio.h>
void add(int a,int b);

[Code]....

i saved it with name PIYUSHAN.cpp.after compiling above program, it shows no errors, that means it get compiled successfully. but when I try to run this program it shows Linker error :

Undefined symbol add(int,int) in module PIYUSHAN.CPP
Linker error : Undefined symbol sub(int,int) in module PIYUSHAN.CPP
Linker error : Undefined symbol mul(int,int) in module PIYUSHAN.CPP
Linker error : Undefined symbol div(int,int) in module PIYUSHAN.CPP