CS 1400 Chap 6

Functions General form; type Name ( parameters ) { … return value ; } parameters is a list of comma-separated declarations

More on functions… Functions can be placed –after boilerplate but before main() simplest –after main() covered later –in another file covered later A function has its own variables!

types… The return value of a function must match the function type. Arguments passed to function parameters must match in type and in position. if either of these rules is neglected, the computer will force (cast) a match.

Value passing… int MyFunc (float a, int b) { int temp = x+y; return temp; } int main() { float x=5.1; int z, y=21; z = MyFunc (x, y);

Value passing diagrams… main() MyFunc() z x y a b temp MyFunc (x, y); 5.121

Examples: FunctionExample Squarecout << Square (21.6); Cubey = Cube (z); Maxcout << Max (a, b); Absy = Abs (x); PrintHeadPrintHead(); GetBetweeny = GetBetween (21, 80); Roundcout << Round (3.567);

Global variables… Variables declared outside of main() or a function are globally accessible. int x; int main() { cout << x; … Local variables may eclipse global variables int x; int main() { int x; cout << x; …

Static variables… Static variables retain their values when a function exits and are only created and initialized once void MyFunc () { static int counter = 0; cout << counter++; } int main() {MyFunc();// outputs 0 MyFunc();// outputs 1 MyFunc();// outputs 2…

Reference parameters… A function using reference parameters can modify corresponding arguments void Swap (int &a, int &b) { int temp = a; a = b; b = temp; } int main() { … Swap (x, y); Swap (cost, rate);

The value passed or copied into a reference parameter is a forwarding address… main() Swap() x y cost rate a b see x in main() see y in main() temp Swap (x, y);

Results… main() Swap() x y cost rate a b see x in main() see y in main() temp

main() Swap() x y cost rate a b see cost in main() see rate in main() temp Swap (cost, rate);

main() Swap() x y cost rate a b see cost in main() see rate in main() temp Results… 3912

Example: Max() The function Max() is intended to determine the maximum value of a list of N numbers input by the user (The argument N is provided by the caller).

Example: MaxMin() The function MaxMin() is intended to determine two values; the maximum and minimum values of a list of 10 numbers input by the user

Functions need not return a value! If a function does not return a value, its type is void and it does not need a return void MyFunc ( int a ) { cout << “the value is: “ << a; cout << “and the square is: “ << a*a; }

Alternate function locations… Functions can be placed below calling functions if the function prototype is above the other functions that call it. A prototype is the first line or title of a function – followed by a semicolon. Functions can be placed in a separate file if the function prototype is above other functions that call it and the function file is included in the project

Example A void Swap (int &a, int &b) { int temp = a; a = b; b = temp; } int main() { …// function Swap() is used here return 0; }

Example B void Swap (int &a, int &b); // function prototype int main() { … // function Swap() is used here return 0; } void Swap (int &a, int &b) { int temp = a; a = b; b = temp; }

Example C FILE A.cpp: void Swap (int &a, int &b); int main() { … // Swap used here return 0; } FILE B.cpp: void Swap (int &a, int &b) { int temp = a; a = b; b = temp; }

Overloading functions… Several functions may have the same name Each function must have a unique signature –name –number and type of parameters Note that the return type of a function is not part of its signature!

Default Arguments A function may specify default values for parameters in its prototype. Example: Example function calls: int TotalPrice (float item_cost; float taxrate = 0.065; int count=1); cout << TotalPrice (5.98); cout << TotalPrice (7.95, 0.075); cout << TotalPrice (3.56, 0.055, 3);

Default Arguments… Only the last or ending arguments may have default values Illegal: cout << TotalCost (4.68,, 4);

Reference Parameters (bis) All arguments for reference parameters must be simple variables – expressions are not allowed; int MyFunc (int x, int& y); … z = MyFunc (5+a, 7*b); OK Illegal!