Functions

defined by types of input parameters, its name, type of return value, and algorithm that computes return value from input values

example:

int add(int a, int b) {
  return a+b;
}

when a function is called, thread of execution continues within code of function

as soon as it returns, code that called the function continues a function returns if:

1. It reaches a return statement
2. It reaches the end of its code block

a void function is allowed to reach end of its code block

a function that has a return value must reach a return statement or throw an exception

Parameters

parameters in declaration of function are called formal parameters parameters in call of function are called actual parameters

Rules of thumb:

1. Use pass-by-value for small objects
2. Use pass-by-const-reference for large objects that you don’t need to modify
3. Return a result rather than modifying parameter through reference
4. Use pass-by-reference only when you have to — when there’s no alternative

pass-by-value:

• copies actual parameters into formal parameters
• formal parameters in function can’t modify anything outside the function
• happens by default
• inefficient with large parameters
• void print(vector<double> v) {}

pass-by-const-reference

• passes address of values (reference)
• efficient, no copying of data
• safe, parameter is const and can’t be overwritten
• void print(const vector<double>& v) {}

pass-by-reference

• if we want to modify contents of parameters, pass by reference
• void init(vector<double>& v) { v[2]=2; }