The file vec.F90 contains a simple user interface for a program that performs basic operations for vectors given by the user (here 3D vectors for simplicity).
Your task is to implement functions for calculating the following operations:
- vector length (norm)
- summation and subtraction between two vectors
- dot product and vector (cross) product between two vectors
Overload them to match with the syntax in vec.F90. Placeholders for these are in vecmod.F90.