1. Alternate Version of STARTING OUT WITH C++ 4th Edition
Chapter 5
Looping
Copyright 2004
Scott/Jones Publishing

2. Topics (continued) 5.8 for Loops 5.9 Deciding Which Loop to Use
5.10 Nested Loops
5.13 Using Loops for Data Validation
Chapter 5 slide 2

3. 5.8 for Loops Top test loop that executes zero or more times
Useful for counter-controlled loop
Format:
for( initialization; test; update )
{ 1 or more statements; }
Required ;
No ; goes here
Chapter 5 slide 3

4. for Loop Mechanics for(initialization; test; update)
{ // {} may be omitted
statement(s); // if loop body contains
} // only 1 statement
Perform initialization
Evaluate test expression
If true, execute statement(s)
If false, terminate loop execution
Execute update, then re-evaluate test expression
Chapter 5 slide 4

5. for Loop Flow of Control
initialization code
update
code
false
test
true
statement(s)
Chapter 5 slide 5

6. for Loop Example int sum = 0, num; for (num = 1; num <= 10; num++)
cout << "Sum of numbers 1 – 10 is "
<< sum << endl;
See pr5-13.cpp
Chapter 5 slide 6

7. for Loop Modifications
Can define variables in initialization code
Their scope is the for loop
Initialization code, test, or update code can contain more than one statement
Separate with commas
Example:
for (int sum = 0, num = 1; num <= 10; num++)
sum += num;
See pr5-14.cpp
Chapter 5 slide 7

8. 5.9 Deciding Which Loop to Use
while: pretest loop (loop body may not be executed at all)
for: pretest loop (loop body may not be executed at all); has initialization and update code; is useful with counters or if precise number of repetitions is known
Chapter 5 slide 8

9. 5.10 Nested Loops
A nested loop is a loop inside the body of another loop
Example:
for (row = 1; row <= 3; row++) {
for (col = 1; col <= 3; col++)
cout << row * col << endl; }
outer loop
inner loop
See pr5-15.cpp
Chapter 5 slide 9

10. Nested Loops Notes
Inner loop goes through all its repetitions for each repetition of outer loop
Inner loop repetitions complete sooner than outer loop
Total number of repetitions for inner loop is product of number of repetitions of the two loops. In previous example, inner loop repeats 9 times
Chapter 5 slide 10

11. 5.13 Using Loops for Data Validation
Loops are the most appropriate structure for
validating user input data
Prompt and read in the data.
Use a top test loop to test if data is valid.
Enter the loop only if data is not valid.
Inside the loop, prompt the user to re-enter the data.
The loop will not be exited until valid data has been entered.
Chapter 5 slide 11

12. Data Validation Loop Example
cout << “Enter a number (1-100) and”
<< “ I will guess it. ”;
cin >> number;
while (number < 1 || number > 100)
{ cout << “Number must be between 1 and 100.”
<< “ Re-enter your number. ”; }
// Code to use the valid number goes here.
See pr5-18.cpp
Chapter 5 slide 12

13. Alternate Version of STARTING OUT WITH C++ 4th Edition
Chapter 5
Looping
Copyright 2004
Scott/Jones Publishing