Review 2

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Review forExam 2
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Chapter 5 Outline

• writing value-returning functions
• program design with value-returning functions
• void functions and program design
• Function calling other functions

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Parameters vs. Arguments
parameters are variables that belong to the
function (in declaration and definition header),
used to receive data from the calling statement.
parameters
arguments appear in the function call, hold the
data to be passed to a function
arguments
parameters
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Parameter and Argument Matching

• A function call creates a memory cell for each
  parameter and then copies the value of the
  matching argument into that cell
• Arguments and parameters are matched from left to
  right based on their positions, i.e., the value
  of the first argument is passed (assigned) to the
  first parameter.

IMPORTANT!
The names of the arguments parameters do not
matter for this purpose Theyd better be of
compatible data types
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Value parameters passing by value

• What were doing here is passing by value
• Argument is evaluated
• Then a copy of that value is passed to the
  corresponding parameter of the called function
• If a function changes the value of one of its
  parameters, that change will stay local to the
  function
• it will NOT affect the arguments value back at
  the point of the call
• There is another way, that lets functions change
  their argument values if we choose to use it
• Reference parameters

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Scope of variables

• The scope of a variable is the portion of the
  program in which statements can use them
• Scope for local variables and value parameters is
  limited to the body of that function
• Scope of (local) variables defined in main is
  limited to the body of main
• Global variables and constants are defined before
  main and can be used in all functions
• Read Section 9.4

include ltiostreamgt const double RATE
5.00 double function (int iHours)int main(
) double salary int hours salary
function(hours) double function(int
iHours) doulbe dSalary dSalary iHours
RATE return dSalary
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void (Non-Value Returning) Functions
declare a void function
call a void function
define a void function
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Chapter 6 Outline

• string variables
• cin and cout streams
• Reading strings with whitespace characters
• getline function
• cin.ignore function

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The string Library

• string variable is a sequence of characters,
  taken together as a unit
• Must include ltstringgt at top of program
• string library comparison, input/output, other
  functions
• Declaring string Variables
• string LastName LastName "Jones"
• String Literals
• Remember, use double-quote marks " for strings
  that appear in the source code.
• do not use " in response to run-time prompt

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Read a value into a string variable

• cin gtgt
• skips over any leading whitespace characters
  (blanks, tabs, newlines)
• copies non-whitespace characters it sees into the
  string variable
• stops when it hits the next whitespace character
• Its impossible to read a string with embedded
  whitespace characters into a single string
  variable using the gtgt operator

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Concatenating strings with
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Function getline

• getline (stream, string)
• stream is an input stream like cin
• string is a string variable
• Input (Reads) up to the next newline character

• read the users name into string variable name
• name would receive the value Jane Doe

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Mixing gtgt and getline
Linux
Windows

• Why didnt the user get a chance to enter her
  name?
• before executing getline(cin, name) the state
  of cin is (Linux)the state of cin is
  Jane Doe (Windows)
• getline assigns a string with no characters to
  name

When the next character in cin is the newline
character, then the call getline(cin, str_var)
assigns null string (i.e., no characters) to
str_var.
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Use the ignore function

• After execution of cin gtgt age
• the only character still in cin is
• After execution cin.ignore(80, \n)
• is discard and there will be no characters in
  cin.

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Chapter 7 Outline

• Looping in programs
• while loops
• for loops
• do-while loops

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The while Loop

• Syntax
• while (Condition)
• Statements
• As long as the Condition is true, keep executing
  Statements in the loop body
• Statements can be either a single statement or a
  group of statements within braces

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Simple while Example
Note in the while loop, initialization is
outside the loop.
n is loop control variable (LCV).

• The Loop Elements
• Initialization n 1
• Test Condition (n lt 3)
• Statement cout ltlt Test " ltlt n ltlt endl
• Update Condition n n 1
• What if the condition is never updated?

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The Infamous Infinite Loop

• A Loop That Never Terminates
• Possible reasons
• Loop specified wrong
• Example control variable can never attain exit
  value
• Never reaches exit condition
• Example forgot to update the control variable
• Bug in the loop body
• Example control variable reset somewhere in
  loop body
• Effect
• May be obvious
• Example output statement within loop
  body (text starts streaming down your screen)
• May be silent
• Just sits there, and sits there, and

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The for Loop

• Shorthand For Use With Fixed-Step Loops
• Syntax
• for (Initialize LCV Test LCV Update LCV)
• Statements
• Execute Initialize LCV
• While Test LCV is true
• Execute Statements
• Execute Update LCV
• Example
• int n
• for (n 0 n lt 10 n)
• cout ltlt n is " ltlt n ltlt endl

NOTE semicolons,not commas!!
// For n from 0 to 10 by 1
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The for vs. the while Constructs

• for (n 0 n lt 10 n)
• cout ltlt n is " ltlt n ltlt endl
• is the same as

Initialization Test Statements Update
n 0 while (n lt 10) cout ltlt n is ltlt n
ltlt endl n
Value of n after the while and for loop?
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Which variables to initialize

• Using for loops to process information for a
  certain number of people, items, or groups of
  data

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• Using variables for the initial and test values
  of the LCV

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The do - while Loop

• do
• Statements
• while (Condition)
• Execute Statements if Condition is true,
  then execute Statements again, ...
• Statements always get executed at least once

(needed)
Statements
false
Test
true
(continue withthe statement following the do
while loop)
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do-while vs. while

• Test at the bottom of the loop
• Loop body must be executed at least once
• Test not done until after execution of body

• Test at the top of the loop
• Loop body executed zero or more times
• If test fails first time through, loop body never
  executes

Coding Style Put the while clause on the same
line as the
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Chapter 8 Outline

• Guidelines for constructing a loop structure
• Loops that exit on completion of the task
• Dont know ahead of time how many times to loop
• Have to recognize exit criterion when it comes up
• Exit a loop using the break statement
• Nested loop

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What to check?

• Initialization
• Check the initial value of loop control or other
  key variables
• Order
• Check where the loop control variables be updated
• Relational Operator
• Check the relational operator in the loop exit
  (condition) test
• lt or lt
• or !
• First and Last Execution of Loop Body

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Multiple Reasons for a Loop Exit

• When there are two or more possible reasons for
  exiting a loop, a compound condition is used in
  the loop exit test.
• Use an if else statement after the loop to
  determine which condition caused the exit

do cout ltlt "The residency status should be
R or N. \n" cout ltlt "Please enter the
residency status (R or N) " cin gtgt
chResStatus while (chResStatus ! 'R'
chResStatus ! 'N') if (chResStatus R)
cout ltlt The student is resident. ltlt
endl else cout ltlt The student is
nonresident. ltlt endl
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The Middle-Exit Loop

• Uses the break Statement to exits innermost loop
  construct
• int Number, Count
• int Sum 0
• while (true)
• cout ltlt "Enter a number "
• cin gtgt Number
• if (Number lt 0)
• break
• Sum Number
• count
• cout ltlt Sum is ltlt Sum ltlt endl
• count ltlt Count is ltlt Count ltlt endl

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Nested Loops - Loop Within a Loop

• int Number, Count
• int Sum 0
• while (true)
• cout ltlt "Enter a number "
• cin gtgt Number
• if (Number lt 0)
• break
• for (int i0 iltNumber i)
• Sum i
• if (Sum gt 10)
• break
• cout ltlt Sum is ltlt Sum ltlt endl

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Nested Loops - Loop Within a Loop
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Chapter 9 Outline

• Reference Parameters

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Reference parameters passing by reference

• Value parameters
• a copy of that value is passed to the
  corresponding parameter of the called function
• If a function changes the value of one of its
  parameters, that change will stay local to the
  function
• it will NOT affect the arguments value back at
  the point of the call

• Reference parameters
• A reference parameter allows a function call to
  give a value to or update the current value of a
  variable argument appearing in the call.
• The ampersand, , between the parameters data
  type and its name, says the parameter is a
  reference parameter

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Reference parameters Passing by Reference
void f(int a, int b) int main() int
x 3, y 5 f(x, y) cout ltlt x ltlt
ltlt y ltlt endl return 0 void f(int a,
int b) a b 1 b 10
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Swapping two values
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Designing Writing Programs

• Assignment 3 (function)
• Assignment 4 (loops)
• Assignment 5 (nested loops)
• Assignment 2 (if else)

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What else to review?

• All the Required Exercises posted on the web site