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If you pass a structure using call-by-value, the function has a local variable that is initialized to a copy of the structure, just as would happen if you passed an integer by value. For example, if print is defined by
void print(Cell c)
{
...
}
then when print(e) is called, the contents
of structure e is copied into a local variable,
c, of type Cell, in the frame for print.
Any change that print makes to c will
only affect that local copy.
Usually, you do not want to copy a structure. It takes time and memory to do that. Instead, you prefer to pass a structure using either call by reference or call by pointer. If you do not intend to change the structure, mark it as const. For example, a more typical definition of print would begin
void print(const Cell& c)
{
...
}
Using type Complex from the preceding page, define function sum(a,b,c) that takes two complex numbers a and b (as in-parameters), and sets out-parameter c equal to the sum of a and b. The definition of the sum is that c.impart = a.impart + b.impart and c.repart = a.repart + b.repart. Answer
A function is allowed to return a structure. Redo the preceding exercise, but this time make sum have only the two in-parameters, and make it return the answer. (Returning a structure requires copying the structure, so it is usually a fairly slow way to do things, but you can do it in places where efficiency is not a big deal.) Answer
Write a function re(z) that returns the real part of Complex number z. Answer
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