Using Free Functions, Study notes of Computer Programming

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Chapter 3

Using Free Functions

3rd Edition

Computing Fundamentals with C++

Rick Mercer

Franklin, Beedle & Associates

Goals

• Evaluate some mathematical and trigonometric functions
• Use arguments in function calls
• Appreciate why programmers divide software into functions
• Read function headings so you can use existing functions

The pow function

• The pow function returns the first argument to the second argument's power pow(2.0, 3.0) returns 2 to the 3rd power ( 3 = 8.0) #include // For the cmath functions #include using namespace std; int main() { double base, power; base = 2.0; power = 4.0; cout << pow(base, power) << endl; cout << pow(- 2 , 3 ) << endl; return 0; }

Function Headings

• Can understand how to use a function if you see the function heading
• General form type functionName ( type arg1 , type arg2, … )
• One function heading

double pow(double base, double power)

• Comments example function calls also help

pow(5.0, 3.0) // evaluates to 125

Evaluate some Function Calls

• Different arguments cause different return values

ceil(0.1)_____ sqrt(16.0)_____

ceil(1.1)_____ sqrt(sqrt(16))_____

pow(2.0, 3)_____ fabs(-1.2)_____

sqrt(4.0)_____ floor(3.99)_____

Rounding to n decimals

• Code that rounds x to n decimal places using the pow and floor functions

x = 456.789;

n = 2;

x = x * pow(10, n); // x ________

x = x + 0.5; // x ________

x = floor(x); // x ________

x = x / pow(10, n); // x ________

Preconditions and Postconditions

• C++ comments that represents a contract between the implementers of a function and the user (client) of that function
• Precondition What the function requires to be true when called
• Postcondition What the function will do if the precondition(s) is/are met

Pre: and Post: conditions

• The preconditions are the circumstances that must be true in order for the function to successfully fulfill the postconditions
• Example Precondition abbreviates to pre: double sqrt(double x) // pre: x >= 0 // post: Returns square root of x
• sqrt(-1.0) evaluates to nan (not a number)

Function Headings

• General form of a function heading: return-type function-name ( parameter-list )

return-type is any C++ type e.g. double int string

function-name is any valid C++ identifier that is not reserved

parameter-list is a set of 0 or more parameters

• General form for declaring parameters: class-name identifier
• Examples

double f(double x)

int max(int j, int k)

string duplicate(string str, int n)

Argument/Parameter Associations

• Example call to max shows that arguments match parameters by position

double max(double x, double y)

cout << max(3.0, - 5.32);

• The value of the 1 st argument is copied to the 1 st parameter, the value of the 2 nd argument to the 2 nd parameter, and so on, like assignments:

x = 3.0;

y = - 5.32;

char and int

• The toupper and tolower functions convert a char to its lower case or upper case equivalent
• Because the return type for both is int instead of char, the functions need to be cast to char with the code (char) to see the character toupper('a') // 65 (char) toupper('a') // A tolower('A') // 97 (char) tolower('A') // a

Summary

• Documented function headings provide the following information:
• The type of value returned by the function
• The function name
• The number of arguments to use in a call
• The type of arguments required in the function call
• Pre- and post-conditions tell us what the function will do if the preconditions are met