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Engineering Problem Solving
with C++, Etter/Ingber
Chapter 3
Control Structures
Engineering Problem Solving with
C++, Second Edition, J. Ingber
1
Control structures
 Algorithm Development
 Conditional Expressions
 Selection Statements
 Repetition Statements
 Structuring Input Loops
Engineering Problem Solving with
C++, Second Edition, J. Ingber
2
Structured Programming
Evaluation of Alternative Solutions
ALGORITHM DEVELOPMENT
Engineering Problem Solving with
C++, Second Edition, J. Ingber
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Algorithm Development
 An algorithm is a sequence of steps for solving a
problem.
 Engineering problem solutions to real world
problems require complex algorithms.
 Development of a good algorithm increases the
quality and maintainability of a solution, and
reduces the overall time required to implement a
correct solution.
Engineering Problem Solving with
C++, Second Edition, J. Ingber
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Top-Down Design
 Top-down design begins with a "big picture"
description of a problem solution in sequential
steps.
 The sequential steps are refined until the steps
are detailed enough to translate to language
statements.
 The refined steps, or algorithm, can be
described using pseudo code or flowcharts.
Engineering Problem Solving with
C++, Second Edition, J. Ingber
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Evaluation of Alternative Solutions
 Most problems have more than one solution.
 There may not be a single best solution, but some solutions
are better than others.
 Elements that contribute to a good solution:
–
–
–
–
–
–
–
correctness
reliability
readability
maintainability
execution speed
memory considerations
user interface
Engineering Problem Solving with
C++, Second Edition, J. Ingber
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Structured Programming
 A structured program is written using simple
control structures, including:
– Sequence – steps are performed one after another.
– Selection – one set of statements is executed if a given
condition is true, a different set of statements, or no
statements at all, is executed if the condition is false.
– Repetition –A set of statements is executed repeatedly
as long as a given condition is true.
Engineering Problem Solving with
C++, Second Edition, J. Ingber
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Structured Programming
 Sequence
 Selection
 Repetition
false
?
true
false
?
true
Engineering Problem Solving with
C++, Second Edition, J. Ingber
? => conditional
expression
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Relational operators
Logical operators
CONDITIONAL EXPRESSIONS
Engineering Problem Solving with
C++, Second Edition, J. Ingber
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Conditional Expressions
 A conditional expression is a Boolean
expression that evaluates to true or false.
 Selection structures and repetition structures
rely on conditional expressions.
 Relational operators and logical
operators are used to form conditional
expressions.
Engineering Problem Solving with
C++, Second Edition, J. Ingber
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Relational Operators
==
!=
<
>
<=
>=
equality
non equality
less than
greater than
less than equal to
greater than equal to
Engineering Problem Solving with
C++, Second Edition, J. Ingber
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Logical Operators
!
&&
||
not
and
or
Engineering Problem Solving with
C++, Second Edition, J. Ingber
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Logical Operators
A
B
A&&B
A||B
!A
!B
0
0
0
0
1
1
0
1
0
1
1
0
1
0
0
1
0
1
1
1
1
1
0
0
Truth table for conditional expressions
0=
Engineering Problem Solving with
C++, Second Edition, J. Ingber
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Operator Precedence
1. < <= > >=
2. == !=
3. &&
4. ||
Engineering Problem Solving with
C++, Second Edition, J. Ingber
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Practice! - evaluate
 (-6<0)&&(12>=10)
true && true
results in true
 (3.0 >= 2.0) || (3.0 >= 4.0)
true || false
results in true
 (3.0 >= 2.0) && (3.0 >= 4.0)
true && false
results in false
Engineering Problem Solving with
C++, Second Edition, J. Ingber
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if statement
switch statement
SELECTION STATEMENTS
Engineering Problem Solving with
C++, Second Edition, J. Ingber
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Selection Statements
 The C++ programming language supports the
implementation of selection with:
– if statements
– switch statements
Engineering Problem Solving with
C++, Second Edition, J. Ingber
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The if statement
if(expression)
statement;
/*single statement executed
if expression is true */
// statement block is executed if expression is true.
if(expression)
{
statement1;
statement2;
…
statement n;
}
Engineering Problem Solving with
C++, Second Edition, J. Ingber
18
The if statement - examples
if (x>0)
++k;
if(x>0)
{
x=sqrt(x);
++k;
}
Engineering Problem Solving with
C++, Second Edition, J. Ingber
19
The if - else statement
if(expression)
statement;
else
statement;
if(expression)
{
statement block
}
else
{
statement block
}
Engineering Problem Solving with
C++, Second Edition, J. Ingber
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The nested if-else
if(x > y)
if(y < z)
k++;
else
m++;
else
j++;
Engineering Problem Solving with
C++, Second Edition, J. Ingber
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Practice!
int x=9, y=7, z=2, k=0, m=0, j=0;
if(x > y)
if(y >z && y>k)
k++;
else
m++;
else
j++;
What are the values of j, k and m?
Engineering Problem Solving with
C++, Second Edition, J. Ingber
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The switch statement
switch(expression)
{
case constant:
statement(s);
break;
case constant:
statement(s);
break;
/* default is optional*/
default:
statement(s);
}
Engineering Problem Solving with
C++, Second Edition, J. Ingber
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The switch statement
 Expression must be of type integer or
character.
 The keyword case must be followed by a
constant.
 break statement is required unless you want
all subsequent statements to be executed.
Engineering Problem Solving with
C++, Second Edition, J. Ingber
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switch statement example
char ch;
int ecount=0, vowels=0, other=0;
cin.get(ch);
while(!cin.eof())
{ switch(ch)
{ case ‘e’: ecount++;
case ‘a’:
case ‘i’:
case ‘o’:
case ‘u’:vowels++;
break;
default: other++;
}//end switch
cin.get(ch);
}//end while
cout << ecount << ‘,’ << vowels << ‘,’ << other << endl;
Engineering Problem Solving with
C++, Second Edition, J. Ingber
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Practice!
Convert these nested if/else statements to a
switch statement:
if (rank==1 || rank==2)
cout << "Lower division \n";
else
{ if (rank==3 || rank==4)
cout << "Upper division \n";
else
{ if (rank==5)
cout << "Graduate student \n";
else
cout << "Invalid rank \n";
}
}
Engineering Problem Solving with
C++, Second Edition, J. Ingber
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while statement
do while statement
for statement
Structuring input loops
REPETITION STATEMENTS
Engineering Problem Solving with
C++, Second Edition, J. Ingber
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Repetition Statements
 The C++ programming language supports the
implementation of repetition with:
– while statements
– do/while statements
– for statements
Engineering Problem Solving with
C++, Second Edition, J. Ingber
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The while statement
false
?
while (expression)
statement;
true
while (expression)
{
statement block
}
Engineering Problem Solving with
C++, Second Edition, J. Ingber
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The do/while statement
do
statement;
while (expression)
do
{
statement block
} while (expression)
true
?
false
Engineering Problem Solving with
C++, Second Edition, J. Ingber
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Practice!
#include <iostream>
using namespace std;
int main()
{
int n=4;
while(n>0)
{
cout << n << endl;
--n;
}
cout << “value of n outside while is “ << n << endl;
return 0;
}
Program Trace:
Output?
Engineering Problem Solving with
C++, Second Edition, J. Ingber
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The for statement
initalize
?
false
increment/
decrement
true
statement(s)
statement(s)
Engineering Problem Solving with
C++, Second Edition, J. Ingber
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The for statement
for(initialization; expression; increment/decrement)
statement;
for(initialization; expression; increment/decrement)
{
statement;
statement;
}
Engineering Problem Solving with
C++, Second Edition, J. Ingber
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The for statement - examples
Alternate solution:
//sum integers from
//sum integers from
//1 to 10 inclusive
//1 to 10
#include<iostream>
#include<iostream>
using namespace std;
using namespace std;
int main()
int main()
{
{
int sum=0;
int sum=0;
for(int i=1;i<11;++i)
for(int i=1;i<=10;i++)
{
sum = sum + i;
sum = sum + i;
cout << sum << endl;
}
return 0;
cout << sum << endl; }
return 0;
}
Engineering Problem Solving with
C++, Second Edition, J. Ingber
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The for statement - example
//sum odd integers from
//1 to n inclusive
#include<iostream>
using namespace std;
int main()
{
int sum=0, n;
cout << "enter non-negative integer: ";
cin >> n;
for(int i=1;i<=n;i+=2)
sum = sum + i
cout << sum << endl;
return 0;
}
Engineering Problem Solving with
C++, Second Edition, J. Ingber
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The for statement - example
//sum odd integers from
//1 to n inclusive
//Alternate Solution
#include<iostream>
using namespace std;
int main()
{
int sum=0, n;
cout << "enter non-negative integer: ";
cin >> n;
for(int i=1;i<=n;++i)
{
if(i%2) sum = sum + i;
}
cout << sum << endl;
return 0;
}
Engineering Problem Solving with
C++, Second Edition, J. Ingber
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Practice!
 Write a program solution to print all
integer values between 1 and n that are
multiples of 5 (ie evenly divisible by 5).
 Compare your solution with another
person's solution.
Engineering Problem Solving with
C++, Second Edition, J. Ingber
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The break statement
 break;
– terminates loop
– execution continues with the first statement following
the loop
Example: What is the output?
for(int i-0; i<=10; ++i)
{
if(i%2) break;
cout << i << endl;
}
Engineering Problem Solving with
C++, Second Edition, J. Ingber
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The continue statement
 continue;
– forces next iteration of the loop, skipping any
remaining statements in the loop
Example: What is the output?
for(int i-0; i<=10; ++i)
{
if(i%2) continue;
cout << i << endl;
}
Engineering Problem Solving with
C++, Second Edition, J. Ingber
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Practice!
//This while loop calculates n!
int nfact=1, n;
cout << "enter positive integer ";
cin >> n;
while(n > 1)
{
nfact = nfact*n;
n--;
}
cout << n << "! = " << nfact << endl;
//What is the output for n=5?
//Write an alternate solution.
Engineering Problem Solving with
C++, Second Edition, J. Ingber
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Structuring Input Loops
 Repetition is useful when inputting data from standard
input or from a file.
Common repetition structures:
counter-controlled
sentinel-controlled
end-of-data controlled
Engineering Problem Solving with
C++, Second Edition, J. Ingber
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Counter-controlled Repetition Structure
i 0
while i < = counter
input data value
//Do something with data value
increment i
end while
Engineering Problem Solving with
C++, Second Edition, J. Ingber
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Sentinel-controlled Repetition Structure
input data value
while data value ! = sentinel value
//Do something with data value
input next data value
end while
Engineering Problem Solving with
C++, Second Edition, J. Ingber
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eof()-controlled Repetition Structure
input data value
while end-of-file is not true
//Do something with input data
input next data value
end while
Engineering Problem Solving with
C++, Second Edition, J. Ingber
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