Chapter 3 - Flow of Control Part II.pdf

Fundamentals of
Computer Programming
Chapter 3
Flow of Control Part II
(Loop Statements)
Chere L. (M.Tech)
Lecturer, SWEG, AASTU
1

Outline
 Introduction to iterative flow control
 Iterative flow controls (Looping statements)
 for loop
 while loop
 do . . . while loop
 Jumping statements
 break, continue, goto
 Program termination statements
 return, exit, abort
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Objectives
 Learn how to use iterative flow control
 Learn how to form Boolean expressions and examine
relational and logical operators
 Design and develop program using loop statements
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1. Introduction to looping
 The loop Statements allow a set of instructions to be performed
repeatedly until a certain condition is fulfilled.
 Following is the general from of a loop statement in most of
the programming languages
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1. Introduction to looping (cont’d)
Part of loop
 Initialization Expression(s)
 initialize(s) the loop
 variables in the beginning of the loop.
 Test Expression
 Decides whether the loop will be executed (if test expression is
true) or not (if test expression is false).
 Update Expression(s)
 update(s) the values of loop variables after every iteration of
the loop.
 The Body-of-the-Loop
 Contains statements to be executed repeatedly.
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Types of loop
 Most programming language provides the following types of loop to
handle looping requirements
Loop Type Description
while loop Repeats a statement or group of statements until a given
condition is true.
It tests the condition before executing the loop body.
for loop Execute a sequence of statements multiple times and
abbreviates the code that manages the loop variable.
do...while loop Like a while statement, except that it tests the
condition at the end of the loop body
nested loops You can use one or more loop inside any another
while, for or do..while loop.
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Chapter 3

Category of loops
1) Pretest and Posttest loops
 Pretest loops (while loop & for loop) - the loop condition checked first,
if false, statements in the loop body never executed.
 Posttest loop (do .. while loop) - the loop condition is checked/tested
after the loop body statements are executed.
 Loop body always executed at least once
2) Count-controlled and Event-Controlled loops
 Count-controlled (for loop) – also called fixed count loop
 Repeat a statement or block a specified number of times
 Used when exactly how many loops want to made
 Event-controlled (while and do-while loop) – also called variable condition loop
 Repeat a statement or block until a condition within the loop
body changes that cause the repetition to stop.
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Types of Event-Controlled Loops
 Sentinel controlled
Keep processing data until a special value (sentinel value)
that is not a possible data value is entered to indicate
that processing should stop.
 End-of-file controlled
Keep processing data or executing statement(s) as long as
there is more data in the file.
 Flag controlled
Keep processing data until the value of a flag changes in
the loop body
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2. while loop
 Syntax
while (repetition condition) {
statement (s);
}
next statement(s);
 Repetition condition
 It is the condition which controls the loop
 Must evaluated to true/false (i.e. Boolean expression)
 Can be formed by combining two or more relational expression with
logical operators
 The statement is repeated as long as the loop repetition condition is true.
 infinite loop - if the loop repetition condition is always true.
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2. while loop (cont’d)
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Chapter 3
Logic of a while loop

EXAMPLE:
2. while loop (cont’d)
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3. for loop
 Syntax
 Condition
 controls the loop and must evaluated to true/false
 Can be formed by combining two or more relational expression with
logical operators
 The statement is repeated as long as the loop repetition condition is true
for ( initialization ; condition ; increment )
{
statement;
}
The initialization is
executed once before the
loopbegins
The statement is executed
until the condition becomes
false
The increment portion is executed at
the end of each iteration
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3. for loop (cont’d)
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statement
true
condition
evaluated
false
increment
initialization
Logic of a for loop

EXAMPLE:
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The for loop Variations
a) Multiple initialization and update expressions
A for loop may contain multiple initialization and/or multiple
update expressions.
These multiple expressions must be separated by commas.
Example:
b) Other for loop forms
for ( ;n < 10; ) if we wanted to specify no initialization and no update expression
for (; n<10; n++)
if we wanted to include an update expression but no initialization
(maybe because the variable was already initialized before).
for (;;)
for(j=25; ;--j)
infinite loop:- Removing either all the expressions or missing condition
or using condition that never get false gives us an infinite loop
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Prefix or postfix increment/decrement
 Reason being that when used alone, prefix operators are faster
executed than postfix
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Empty loop
 If a loop does not contain any statement in its loop-body, it is said
to be an empty loop:
for(j=25; (j);--j) //(j) tests for non zero value of j.
 If we put a semicolon after for’s parenthesis it repeats only for
counting the control variable.
 And if we put a block of statements after such a loop, it is not a
part of for loop.
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4. do . . . while loop
 Syntax
do {
statement (s);
} while (repetition condition)
next statement(s);
 It is similar to while loop except it is posttest loop
 The statement is first executed.
 If the loop repetition condition is true, the statement is repeated.
 Otherwise, the loop is exited.
 The repetition condition should be Boolean expression
 Used when your program need to be executed at least one iteration
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4. do . . . while loop (cont’d)
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Logic of a do . . while loop

EXAMPLE:
4. do . . . while loop (cont’d)
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 Nested loops consist of an outer loop with one or more inner loops
5. Nested loop
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The above loop will run for 100*50 iterations

EXAMPLE:
5. Nested loop (cont’d)
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6. Jumping Statements
(a) The goto statement
 It can transfer the program control anywhere in the program.
 The target destination is marked by a label.
 The target label and goto must appear in the same statement.
 The syntax:
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goto label;
………
………
label:

6. Jumping Statements (cont’d)
(b) The break statement
 Enables a program to skip over part of the code.
 It terminates the smallest enclosing while, do-while and for
loop statements.
It skips the rest of the loop and jumps over to the
statement following the loop.
 The figures on the next slide explains the working of a break
statement :
 Aslo use along with switch as discussed under the selection
control section
 Syntax:
break;
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How break statement works with loops
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Chapter 3
while(condition)
{
statement1;
if(val>2000)
break;
:
statement2;
}
statement3;
for(initialization; condition; update)
{
statement1;
if(val>2000)
break;
:
statement2;
}
statement3;
Note:
• The break statement can be used in similar fashion with do…while loop also

Example of break statement
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Chapter 3

(c) The continue statement
 Enables a program to skip over part of the code.
 works somewhat like the break statement.
 For the for loop, continue causes the conditional test and
increment portions of the loop to execute.
 For the while and do...while loops, program control
passes to the conditional tests.
 Syntax:
continue;
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Example of continue statement
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As you can see on the output
below the program jumps
printing 3 & 6 which are
factor of 3

Examples (break and continue
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7. Terminating Program
(a) The return statement
 As you seen in the main() function it terminate the program
and return control back to the Operating System
 Syntax: return returnValue;
(b) The exit() function
 Used to terminate the program normally and return the
control to the Operating System.
 Syntax: exit(int exitCode);
 Avaliable in <cstdlib> library (ported from C's "stdlib.h")
(c) The abort() function
 The same as exit() function but except it used to terminate the
program abnormally.
 Syntax: abort(int exitCode);
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7. Terminating Program
Example
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if (errorCount > 10)
{
cout << "too many errors" << endl;
exit(-1); // Terminate the program
// also you can use abort(-1); instead to
terminate the program abnormally
}
if (errorCount > 10)
{
cout << "too many errors" << endl;
return 1;
}

Exercises (MCQ)
(1) The statement i++; is equivalent to
(a) i = i + i; (b) i = i + 1; (c) i = i - 1; (d) i --;
(2) What's wrong? for (int k = 2, k <=12, k++)
(a) the increment should always be ++k
(b) the variable must always be the letter i when using a for loop
(c) there should be a semicolon at the end of the statement
(c) the commas should be semicolons
(3) A looping process that checks the test condition at the end of loop?
(a) for while (b) do-while (c) while (d) none
(4) A looping process is best used when the number of iterations is
known
(a) for while (b) do-while (c) while (d) all are require
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Chapter 3

Exercises (MCQ)
(5) A continue statement causes execution to skip to
(a) The return 0; statement
(b) The first statement after the loop
(c) The statement following the continue statement
(d) The next iteration of the loop
(6) A break statement causes execution to skip to
(a) The return 0; statement
(b) The first statement after the loop
(c) The statement following the continue statement
(d) The next iteration of the loop
(e) The statement outside the loop
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Chapter 3

Reading Resources/Materials
Chapter 7 & 8:
 Diane Zak; An Introduction to Programming with C++ [8th
Edition], 2016 Cengage Learning
Chapter 5:
 Gary J. Bronson; C++ For Engineers and Scientists [3rd
edition], Course Technology, Cengage Learning, 2010
Chapter 2 (section 2.4):
 Walter Savitch; Problem Solving With C++ [10th edition],
University of California, San Diego, 2018
Chapter 4 & 5:
 P. Deitel , H. Deitel; C++ how to program [10th edition],
Global Edition (2017) 34
Chapter 3

Thank You
For Your Attention!!
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Chapter 3

Chapter 3 - Flow of Control Part II.pdf

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