002 - Forward Declaration

• Declare the symbol before defining the implementation. This includes class, functions, or variables.
• This helps the compiler understand the type, size, and existence of symbols.
• Useful when there is cyclic dependencies, or to reduce compilation time by avoiding unnecessary header inclusions.

int add(int a, int b); // forward declaration
 
int main() {
    int result = add(2, 3);
    return 0;
}
 
int add(int a, int b) {
    return a + b;
}

Note: You cannot forward declare enum and typedef. This is because there is not a separate declaration and definition for these.