How can template increase the code reusebility in c plus plus?

Templates encourage generic programming. When classes or functions only differ by type, there is no need to write the same implementations over and over -- the compiler generates the functions or classes from the template. You can also cater for specialisation, so if you need a more specific implementation for pointers to types rather than actual types, you can provide the code to cater for this, without the need to duplicate already existing code that caters for all types.