Understanding Functions in C++: Headings, Prototypes, Calls, and Parameters, Slides of Advanced Computer Programming

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Chapter 7

Functions

Chapter 7 Topics

• Writing a Program Using Functional

Decomposition

• Writing a Void Function for a Task
• Using Function Arguments and Parameters
• Differences between Value Parameters and

Reference Parameters

• Using Local Variables in a Function
• Function Preconditions and Postconditions

Function Calls

One function calls another by using the name

of the called function followed by()s that

enclose an argument list, which may be

empty

A function call temporarily transfers control

from the calling function to the called

function

Function Call Syntax

FunctionName( Argument List )

The argument list is a way for functions to communicate

with each other by passing information

The argument list can contain 0, 1, or more arguments,

separated by commas, depending on the function

What is in a heading?

int Cube (int n)

type of value returned

name of function

parameter list

Prototypes

A prototype looks like a heading but must

end with a semicolon, and its parameter

list needs only to contain the type of each

parameter

int Cube(int ); // Prototype

#include int Cube(int); // prototype using namespace std; void main() { int yourNumber; int myNumber; yourNumber = 14; myNumber = 9; cout << “My Number = “ << myNumber; cout << “its cube is “ << Cube( myNumber) << endl; cout << “Your Number = “ << yourNumber; cout << “its cube is “ << Cube( yourNumber) << endl; } arguments

Successful Function Compilation

Before a function is called in your program,

the compiler must have previously

processed either the function’s prototype

or the function’s definition (heading and

body)

Example

Write a void function called DisplayMessage(),

which you can call from main(), to describe the

pollution index value it receives as a parameter

Your city describes a pollution index

less than 35 as “Pleasant”,

35 through 60 as “Unpleasant”,

and above 60 as “Health Hazard”

parameter

void DisplayMessage(int index) { if(index < 35) cout << “Pleasant”; else if(index <= 60) cout << “Unpleasant”; else cout << “Health Hazard”; }

Return Statement

return; // No value to return

• Is valid only in the body block of a void function

• Causes control to leave the function and

immediately return to the calling block, leaving any

subsequent statements in the function body

unexecuted

Header Files

Header Files contain

• Named constants like

const int INT_MAX = 32767;

• Function prototypes like

float sqrt(float);

• Classes like

string, ostream, istream

• Objects like

cin, cout

Value-Returning Functions #include int Square(int); // Prototypes int Cube(int); using namespace std; int main() { cout << “The square of 27 is “ << Square(27) << endl; cout << “The cube of 27 is “ << Cube(27) << endl; return 0; } function calls 19

Rest of Program int Square(int n) // Header and body { return n * n; } int Cube(int n) // Header and body { return n * n * n; }