Describe the purpose of the break statement and the type of problem for which it is well suited.

Nested loops

Nested loops are useful when for each pass through the outer loop, you need to repeat some action on the data in the outer loop. For example, you read a file line by line and for each line you must count how many times the word “the” is found. The outer loop would read the lines and the inner loop would search each line for “the” by looping through the words in the line.

Breaking out of a loop

The C++ statement called break provides a way to break out a loop early. The break statement is placed within the body of the loop usually as part of an if statement.

Example

In the example, the loop is set to run a maximum of 50 times but the user can quit the loop at any time by specifying a specific input, q in this case.

Should you use break?

The use of break statements is not recommended. We expect the iteration of a loop to be controlled by the true/false statements in the while and do-while and the for loop header sections. Adding a means to suddenly stop the loop outside of the normal approach can make code difficult to understand and debug.

We can rewrite the above code to stop when the user enters q without having to use a break statement such as follows.

Using break in a nested loop

In a nested loop, a break statement only stops the loop it is placed in. Therefore, if a break is placed in the inner loop, the outer loop still continues. However, if the break is placed in the outer loop, all of the looping stops.

Video lecture

Nested Loops - by Jennifer Parham-Mocello

Deciding which loop to use?

Go into detail in the first topic. Include images or videos as needed to add clarity. For definitions and easily enumerated things consider using a collapsible list.

The while loop

Choose a while loop when

• You want the option of not looping at all. Since the while loop is a pretest loop, if the initial test of the true/false expression is false, the loop is skipped.
• You don’t know how many times you need to loop. Examples of these types of situations include validating and inputting proper user input, reading values from a file (see later sections of this document), and asking the user for input with the option to stop at any point

The do while loop

Use a do while loop when

• You want to execute the loop statements at least once such as offering a repeating menu to a user.
• You don’t know how many more times you need to loop such as described for the while loop.

The for loop

Since the for loop requires initialization, test, and update elements, it is ideal for situations where you know how many times the loop must iterate.

Video lectures

Looping Recap - by Jennifer Parham-Mocello

Errors and Debugging - by Jennifer Parham-Mocello