PowerPoint Presentation

Project 1 Due Date: September 25th

Quiz 4 is due September 28thQuiz 5 is due October2th

1Control Structures II (Repetition)2Why Is Repetition Needed?Repetition allows efficient use of variablesCan input, add, and average multiple numbers using a limited number of variablesFor example, to add five numbers:Declare a variable for each number, input the numbers and add the variables togetherCreate a loop that reads a number into a variable and adds it to a variable that contains the sum of the numbers

3while Looping (Repetition) StructureSyntax of the while statement:

expression acts as a decision maker and is usually a logical expression statement is called the body of the loop The parentheses are part of the syntax

4while Looping (Repetition) Structure (contd.)

5while Looping (Repetition) Structure (contd.)

6The body of the while executes when the expression evaluates to trueThe expression checks whether a variable called loop control variable (LCV) satisfies certain conditionPrevious example i was LCVLCV should be initialized and eventually make the expression evaluate to false(We do this by updating LCV)

7Generally while loops are written in the following form:/*initialize loop control variable*/while (expression){ /*expression tests LCV*/

//update LCV

}

8while Looping (Repetition) Structure (contd.)

9Case 1: Counter-Controlled while LoopsWhen you know exactly how many times the statements need to be executed Use a counter-controlled while loop

10ExampleCh5_CounterControl.cpp11Case 2: Sentinel-Controlled while LoopsSentinel variable is tested in the condition Loop ends when sentinel is encountered

12ExampleCh5_SentinelControl.cpp13Case 3: Flag-Controlled while LoopsFlag-controlled while loop: uses a bool variable to control the loop

14ExampleCh5_FlagControlledLoop.cpp15Case 3: Flag-Controlled while LoopsFlag-controlled while loop: uses a bool variable to control the loop

16ExampleCh5_FlagControlledLoop.cpp17Case 4: EOF-Controlled while LoopsEnd-of-file (EOF)-controlled while loop: when it is difficult to select a sentinel value

18eof FunctionThe function eof can determine the end of file statuseof is a member of data type istreamSyntax for the function eof:

Ch5_EOFControlledLoop.cpp

19

for Looping (Repetition) Structurefor loop: called a counted or indexed for loopSyntax of the for statement:

The initial statement, loop condition, and update statement are called for loop control statements

20for Looping (Repetition) Structure (contd.)

21for Looping (Repetition) Structure (contd.)

22for Looping (Repetition) Structure (contd.)

23for Looping (Repetition) Structure (contd.)The following is a semantic error:

24The following is a legal (but infinite) for loop:for (;;) cout