50.2 Control flow exercises

50.2.1Loop exercise¶

let mut n = 0;
loop {
  n += if n % 2 == 0 { 3 } else { 1 };
  println!("{n}");
  if n > 30 {
    break;
  }
}

3

4

7

8

11

12

15

16

19

20

23

24

27

28

31

50.2.2Checker¶

Here are the two for loops needed to draw the grid:

for i in 0..20 {
  for j in 0..i {
    print!("{}", if (i+j)%2==0 {'X'} else {' '});
  }
  println!();
}

X 

 X 

X X 

 X X 

X X X 

 X X X 

X X X X 

 X X X X 

X X X X X 

 X X X X X 

X X X X X X 

 X X X X X X 

X X X X X X X 

 X X X X X X X 

X X X X X X X X 

 X X X X X X X X 

X X X X X X X X X 

 X X X X X X X X X 

50.2.3Multiple search in a string¶

We define the letters and the string:

:clear

let s = "abcdefghijklmnop";
let letters = ['c', 'a', 't', 'z', 'h'];

We loop on each letter to search for, and test the result of find() using if let Some(...):

for letter in letters {
  if let Some(index) = s.find(letter) {
    println!("Found {letter} at index {index}.");
  }
}

Found c at index 2.

Found a at index 0.

Found h at index 7.

50.2.4Iterating over results¶

We define the string variable:

:clear

let s = "abc\nde\nfghi\njklm\nnop\n";

We store the iterator returned by lines():

let mut lines = s.lines();

Couldn't automatically determine type of variable `lines`.
Please give it an explicit type.

We use the while let construct to iterate over all results until the end (None value):

while let Some(line) = lines.next() {
  println!("{line}");
}