No Slide Titleelkadi/Slides/CSCE 106/CSCE 1001 Chapter 5… · Title: No Slide Title Author: Addison Wesley Created Date: 6/15/2016 12:25:00 PM

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Chapter 5

Functions for All Subtasks


Value and Reference Parameters

Functions can

return no value

type void

return exactly one value

return statement

function type

return more than one value

type void

reference parameters


Function to compute sum and average


Function to compute sum and average (continued)


Function computeSumAve

Two input parameters

num1, num2

Two output parameters

sum, average

& indicates output parameters

Function call

computeSumAve(x, y, sum, mean);


Argument Correspondence

Actual Argument

x

y

sum

mean

Corresponds to

Formal Argument

num1 (input)

num2 (input)

sum (output)

average (output)


Call-by-Value and Call-by-Reference

Parameters

& between type and identifier defines a

parameter as output mode (pass by reference)

no & in a parameter’s declaration identifies input

mode (pass by value)

Compiler uses info in parameter declaration list

to set up correct argument-passing

mechanism


Data areas after call to computeSumAve (before execution)


Data areas after execution of computeSumAve


Notes on Call-by-Reference

Place the & only in the formal parameter list -not in the actual parameter list

Place the & also in the prototype:

void computeSumAve(float, float, float&, float&);

Note that this is a void function


When to Use a Reference or a Value

Parameter

If information is to be passed into a function and

doesn’t have to be returned or passed out of the

function, then the formal parameter representing

that information should be a value parameter

(input parameter)



Parameter

If information is to be returned to the calling

function through a parameter, then the formal

parameter representing that information must be

a reference parameter (output parameter).



Parameter

If information is to be passed into a function,

perhaps modified, and a new value returned,

then the formal parameter representing that

information must be a reference parameter

(input/output parameter)

Note: C++ does not distinguish between output

parameters and input/output parameters


Program Style

Formal parameter list often written on multiple

lines to improve readability.

Value parameters first, followed by reference

parameters

Comment each parameter to identify its use


Function to order three numbers


Function to order three numbers (continued)

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No Slide Titleelkadi/Slides/CSCE 106/CSCE 1001 Chapter 5… · Title: No Slide Title Author: Addison Wesley Created Date: 6/15/2016 12:25:00 PM