Why do i encounter 'undefined reference to...' in c++?

Example:

void printHello();

int main() {
    printHello();
    return 0;
}

This error typically means you declared a function but forgot to provide its definition.

Solution:

Provide the missing function definition.

void printHello() {
    std::cout << "Hello World!" << std::endl;
}

int main() {
    printHello();
    return 0;
}