This lab serves multiple goals:
- To introduce increment and decrement operators,
- To understand the difference between prefix and postfix operators,
- To help you implement your first
while loops, and
- (Optional) to write your first complex loops.
Increment and Decrement Operators
Preamble
Start by answering the following, assuming an int variable i has
been initialized and that its current value is 5.
- What does
i++ do to i?
- What does
i-- do to i?
- In your own words, can you explain the difference between
++i and
i++?
Solution:
1. `i++` increments the value of `i` by 1; if the value of `i` was 5,
it would become 6.
2. `i--` decrements the value of `i` by 1; if the value of `i` was 5,
it would become 4.
3. An explanation can be found [in this
post](https://stackoverflow.com/q/24853). In short, `++i` “gives
back” the value of `i` *after* it had been incremented by 1, while
`i++` “gives back” the value of `i` *before* it has been
incremented. This makes a difference if `i++` or `++i` is part of a
larger statement. The next exercises will illustrate this principle.
Observe and Confirm
Download, extract, open in your IDE, and read the following
code. Then, compile and execute
it. Study the output carefully to make sure you understand the mechanism
of the increment and decrement operators.
Compare your answers from the previous section to what you observe in
the output. Do your answers correspond to what you observe in the
output?
Exercise
For each of the following, determine the final value of n and x.
int x = 5;
int n = x + x++;
int x = 5;
int n = ++x + ++x;
Solution:
You can download, extract, open in your IDE, and execute [the following
code](./code/projects/IncrementSolution.zip) to check that the answers
are:
``` text
n is now 5.
x is now 6.
n is now 6.
x is now 6.
n is now 10.
x is now 6.
n is now 13.
x is now 7.
```
If you read the source code, you can see that the order of evaluation is
quite difficult to follow. Actually, the way the sum operator `+` and
the increment operator `++` interact is sometimes *undefined*, meaning
that the result may vary from one programming language to another (or
worst, from one *version* to another): you can read more about this
[here](https://stackoverflow.com/a/3458842) of
[there](https://stackoverflow.com/a/4176333) (Disclaimer: those are
*very* technical discussions, much more advanced than [the official
documentation](https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/operators/arithmetic-operators#increment-operator-)
could lead to think).
In short: software developers generally avoid this type of “nested”
operations altogether, and use increment or decrement operators more
scarsely!
First While Loops
The following asks you to write a series of while loops performing
simple tasks. The solution to the first question is in this
archive, but it is recommended to try it
on your own first.
- Write a
while loop that displays the integers between $1$ and
$100$ on the screen with a space between each number.
- Write a
while loop that displays the integers between $100$ and
$-100$ on the screen, in decreasing order, with a space between each
number.
- Write a
while loop that displays the * (asterisk symbol)
character 100 times on the screen.
- Modify your previous loop, so that a new line character is displayed
on the screen every time 10 asterisk symbols have been displayed on
the screen.
To clarify, your program should display the following on the screen
(this example has a space after each asterisk symbol for display
purposes):
* * * * * * * * * *
* * * * * * * * * *
* * * * * * * * * *
* * * * * * * * * *
* * * * * * * * * *
* * * * * * * * * *
* * * * * * * * * *
* * * * * * * * * *
* * * * * * * * * *
* * * * * * * * * *
Pushing Further (Optional)
Here are additional pattern problems, similar to the last one from the
previous section. You are asked to generate these patterns using a
while loop for each.
- Triangle:
*
* *
* * *
* * * *
* * * * *
* * * * * *
* * * * * * *
* * * * * * * *
* * * * * * * * *
* * * * * * * * * *
- Triangle of numbers
1
222
33333
4444444
555555555
- Upside-down binary triangle