1. Engineering Problem Solving with C++, Etter/Ingber
Chapter 3
Control Structures
Engineering Problem Solving with C++, Second Edition, J. Ingber

2. Engineering Problem Solving with C++, Second Edition, J. Ingber
Control structures
Algorithm Development
Conditional Expressions
Selection Statements
Repetition Statements
Structuring Input Loops
Engineering Problem Solving with C++, Second Edition, J. Ingber

3. Algorithm Development
Structured Programming
Evaluation of Alternative Solutions
Algorithm Development
Engineering Problem Solving with C++, Second Edition, J. Ingber

4. 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

5. Engineering Problem Solving with C++, Second Edition, J. Ingber
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

6. 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

7. 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

8. Structured Programming
Sequence
Selection
Repetition ?
false
true ?
true
false
? => conditional expression
Engineering Problem Solving with C++, Second Edition, J. Ingber

9. Conditional Expressions
Relational operators
Logical operators
Conditional Expressions
Engineering Problem Solving with C++, Second Edition, J. Ingber

10. 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

11. Engineering Problem Solving with C++, Second Edition, J. Ingber
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

12. Engineering Problem Solving with C++, Second Edition, J. Ingber
Logical Operators
! not
&& and
|| or
Engineering Problem Solving with C++, Second Edition, J. Ingber

13. Engineering Problem Solving with C++, Second Edition, J. Ingber
Logical Operators A B
A&&B
A||B !A !B 1
Truth table for conditional expressions
0 =
Engineering Problem Solving with C++, Second Edition, J. Ingber

14. Engineering Problem Solving with C++, Second Edition, J. Ingber
Operator Precedence
< <= > >=
== !=
&& ||
Engineering Problem Solving with C++, Second Edition, J. Ingber

15. Engineering Problem Solving with C++, Second Edition, J. Ingber
Practice! - evaluate
(-6<0)&&(12>=10)
(3.0 >= 2.0) || (3.0 >= 4.0)
(3.0 >= 2.0) && (3.0 >= 4.0)
true && true
results in true
true || false
results in true
true && false
results in false
Engineering Problem Solving with C++, Second Edition, J. Ingber

16. Engineering Problem Solving with C++, Second Edition, J. Ingber
if statement
switch statement
Selection Statements
Engineering Problem Solving with C++, Second Edition, J. Ingber

17. Engineering Problem Solving with C++, Second Edition, J. Ingber
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

18. Engineering Problem Solving with C++, Second Edition, J. Ingber
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

19. The if statement - examples
if (x>0)
++k;
if(x>0) {
x=sqrt(x); }
Engineering Problem Solving with C++, Second Edition, J. Ingber

20. Engineering Problem Solving with C++, Second Edition, J. Ingber
The if - else statement
if(expression)
statement;
else
if(expression) {
statement block }
else
Engineering Problem Solving with C++, Second Edition, J. Ingber

21. Engineering Problem Solving with C++, Second Edition, J. Ingber
The nested if-else
if(x > y)
if(y < z)
k++;
else
m++;
j++;
Engineering Problem Solving with C++, Second Edition, J. Ingber

22. Engineering Problem Solving with C++, Second Edition, J. Ingber
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++;
j++;
What are the values of j, k and m?
Engineering Problem Solving with C++, Second Edition, J. Ingber

23. Engineering Problem Solving with C++, Second Edition, J. Ingber
The switch statement
switch(expression) {
case constant:
statement(s);
break;
/* default is optional*/
default: }
Engineering Problem Solving with C++, Second Edition, J. Ingber

24. Engineering Problem Solving with C++, Second Edition, J. Ingber
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

25. 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
}//end while
cout << ecount << ‘,’ << vowels << ‘,’ << other << endl;
Engineering Problem Solving with C++, Second Edition, J. Ingber

26. Engineering Problem Solving with C++, Second Edition, J. Ingber
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";
   { if (rank==5)
cout << "Graduate student \n";
cout << "Invalid rank \n"; }
Engineering Problem Solving with C++, Second Edition, J. Ingber

27. Repetition Statements
while statement
do while statement
for statement
Structuring input loops
Repetition Statements
Engineering Problem Solving with C++, Second Edition, J. Ingber

28. 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

29. Engineering Problem Solving with C++, Second Edition, J. Ingber
The while statement ?
true
false
while (expression)
statement; {
statement block }
Engineering Problem Solving with C++, Second Edition, J. Ingber

30. The do/while statement?
true
false do
statement;
while (expression) {
statement block
} while (expression)
Engineering Problem Solving with C++, Second Edition, J. Ingber

31. Engineering Problem Solving with C++, Second Edition, J. Ingber
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

32. Engineering Problem Solving with C++, Second Edition, J. Ingber
The for statement
initalize ?
false
increment/
decrement
true
statement(s)
statement(s)
Engineering Problem Solving with C++, Second Edition, J. Ingber

33. Engineering Problem Solving with C++, Second Edition, J. Ingber
The for statement
for(initialization; expression; increment/decrement)
statement; { }
Engineering Problem Solving with C++, Second Edition, J. Ingber

34. The for statement - examples
Alternate solution:
//sum integers from
//1 to 10
#include<iostream>
using namespace std;
int main() {
int sum=0;
for(int i=1;i<=10;i++)
sum = sum + i;
cout << sum << endl;
return 0; }
//sum integers from
//1 to 10 inclusive
#include<iostream>
using namespace std;
int main() {
int sum=0;
for(int i=1;i<11;++i)
sum = sum + i; }
cout << sum << endl;
return 0;
Engineering Problem Solving with C++, Second Edition, J. Ingber

35. 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

36. 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

37. Engineering Problem Solving with C++, Second Edition, J. Ingber
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

38. Engineering Problem Solving with C++, Second Edition, J. Ingber
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

39. The continue statement
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

40. Engineering Problem Solving with C++, Second Edition, J. Ingber
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

41. 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

42. Counter-controlled Repetition Structure
while i < = counter
input data value
//Do something with data value
increment i
end while
Engineering Problem Solving with C++, Second Edition, J. Ingber

43. 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

44. 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