Level 1 / C# Fundamentals / fundamental 4 of 7
Repeating work with loops
A loop runs the same block again and again, which is exactly what you are doing in these drills. You will write the three loops C# developers use constantly, then put if statements and running totals inside them.
Understand the idea
for: when you know the count
for (int i = 0; i < 5; i++) has three parts separated by semicolons: start the counter, keep going while this is true, and what to do after each pass. Counting from 0 with < is the C# habit because collections start at index 0.
while: until something changes
while (condition) checks first and repeats as long as the condition stays true. Something inside the loop has to move toward false, or the loop never ends.
foreach: every item in a collection
foreach (int score in scores) hands you each item in turn without a counter. Use break to leave any loop early once you have what you need.
English to C#
“Count from 0 to 4 and print i each time.”
for (int i = 0; i < 5; i++){Console.WriteLine(i);}
- int i = 0
- start the counter at 0
- i < 5
- keep going while this is true
- i++
- after each pass, add 1
- { ... }
- the work repeated each pass
Rep 1 of 12
Copy itIn English
Count from 0 to 4 with a for loop and print i each time.
Type the code shown below. Watch it turn green as you go.
for (int i = 0; i < 5; i++){Console.WriteLine(i);}
Waiting for you to type · 0 of 23 pieces
Ctrl+Enter checks or moves on. Tab indents. Paste is off on purpose: your hands are learning this too.
Reps
0 of 12 done
Reps unlock in order, because each one builds on the last.
How your code is checked
Drills compare what you type with known-correct C#, token by token. Spacing, line breaks, and comments do not matter; spelling, case, and punctuation do. It is not a compiler, so it accepts the listed spellings of each answer and nothing else.
Try it in a real .NET project
Print a multiplication table from 1 to 10 using a for loop inside another for loop. Then rewrite the outer loop as a while loop, and finally keep asking for input in a while loop until the user types quit.
Check your understanding
for (int i = 0; i <= 5; i++) and for (int i = 0; i < 5; i++) differ by one character. How many times does each run?
Show the explanation
The first runs six times (0 through 5) and the second runs five times (0 through 4). Off-by-one mistakes like this are the most common loop bug, which is why counting from 0 with < Length or < Count is the standard habit.
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