C++ crash course
Class 8
statements, sort, flight times
program
Agenda
Last week: operators, expressions
This week:
•Finishing the basics - statements
– new control flow statements
– a simple sort - Insertion
•Flight times program (due Wednesday 10pm)
– What’s the best flight to take?
•Mazes program (due Friday 10pm)
– Given a maze, what’s the best path through it?
•Exam on Friday
– Much like the last one, covering all the material in the
three weeks
Statements
• A statement in C++ is really just a line of code,
ending with a semicolon
• We’ve gone over a lot of statements:
– if
– while
– for
• Let’s talk about a few others
– switch / case
– break, continue
switch / case
• If / else statements aren’t always the cleanest
way to change how a program acts
• switch statements help deeply nested if / else
logic
switch / case
Writing a program:
•Read each character until there are no more
characters
•Compare each character to the set of vowels
•If the character matches one of the vowels, add
1 to that vowel’s count
•Display the results
switch / case
How would we write the program with if / else
statements?
switch / case
• It’s also possible to do this much more easily with a switch /
case
• syntax:
switch (var) {
case const_or_literal:
// do something
break;
case const_or_literal2:
...
}
How can we change our character reading program to use
switch / case?
switch / case
• switch / case is a little tricky though, because
once execution enters a certain point in a
switch / case, it will continue until it
encounters “break”
• make sure you put a break at the end of every
case unless you want to do strange things 
Let’s change our program:
Use switch / case syntax to count ANY vowel
switch / case
• Using the default label is like having an else: execution
will go there if it doesn’t match any other case
• Switch expressions can be anything, but will be
converted to ints
• Case labels must be constant integral types
// bad
case 3.14:
case ival:
break, continue
• Some loops you only want to continue until a
certain thing happens
• Searching a vector for a value, we don’t want
to keep searching once we’ve found it
• Adding a break in the middle of a loop will exit
the loop
• Adding a continue in the middle of a loop will
go to the next execution of a loop (stops
current execution and goes to the next round)
break, continue
• break can only occur inside of switch
statements or loops (while, for)
• can occur inside of if statements when they
are nested inside of switch statements or
loops
break, continue
How might we search an int vector using the
break statement?
We want to find an instance of value in the
vector, and add 1 to it afterwards
insertion sort
• There are a number of ways to sort a set of
numbers, or other items
• We’ll talk about insertion sort as a simple
example
How do we sort these numbers with insertion
sort?
5 87 14 23 62 54 10 19
insertion sort
• Sort of similar to how people sort cards
• Take each element as it’s encountered, put it
in the right place in the sorted list
• Intuitive idea; how can we get a computer to
do it?
Designing Programs
• We have a whole lot of pieces now!
• Let’s write something useful with it 
• Flight Times program
– from a set of inputs, determine what the best
(shortest), average, and worst (longest) flight
times are from a set of inputs
Flight Times Program
• Inputs
how many flights? 5
enter flight times in military HHMM format, one per line
1030 1415
1535 1800
2523 2304
0530 0835
0605 1270
invalid flight times: 2523-2304
invalid flight times: 0605-1270
shortest flight: 1535-1800, elapsed time 2 hrs 25 mins
longest flight: 1030-1415, elapsed time 3 hrs 45 mins
average flight time: 3 hrs 5 mins
Flight Times Program
• First work out the algorithm
– What steps do we need to take to solve the
problem?
• Next work out the way to code the solution
– What data structures do we need?
– What functions should we write?
– What classes do we need?
• Try coding the solution!
Flight Times Program
• Given the input:
1030 1415
...how are we going to parse that?
Closing
• FlightTimes spec and base code will go up
before tomorrow
• Tomorrow: we work through the rest of
FlightTimes
– also: short intro to basic debugging
• You’ll get two more non-required homeworks,
one due tomorrow and one due Thursday (for
practice with the concepts)
• FlightTimes due Wednesday 10pm