We have used three kinds of absolute value function: abs, labs, and fabs.
These functions differ only in the type of their argument. It might be better
to have a function template for the absolute value function. Give a function
template for an absolute value function called absolute. The template
will apply only to types for which <>
negation operator is defined, and for which the constant 0 can be used in
a comparison with a value of that type. Thus, the function absolute can be
called with any of the number types, such as int, long, and double. Give
both the function declaration and the function definition for the template.