Add hints to the variable bindings exercises

This commit is contained in:
Carol (Nichols || Goulding) 2015-09-17 19:16:30 -04:00
parent 9cf4958982
commit dbfab88e61
5 changed files with 151 additions and 8 deletions

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@ -17,10 +17,10 @@ If you need more help or would like to compare solutions, you can ask in [#rust
[Relevant chapter in The Rust Programming Language](https://doc.rust-lang.org/stable/book/variable-bindings.html) [Relevant chapter in The Rust Programming Language](https://doc.rust-lang.org/stable/book/variable-bindings.html)
- ["variables1.rs"](http://play.rust-lang.org/?code=%2F%2F+Make+me+compile%21%0A%0Afn+main%28%29+%7B%0A++++x+%3D+5%3B%0A++++println%21%28%22x+has+the+value+%7B%7D%22%2C+x%29%3B%0A%7D%0A) - ["variables1.rs"](http://play.rust-lang.org/?code=%2F%2F+Make+me+compile%21+Scroll+down+for+hints+%3A%29%0A%0Afn+main%28%29+%7B%0A++++x+%3D+5%3B%0A++++println%21%28%22x+has+the+value+%7B%7D%22%2C+x%29%3B%0A%7D%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%2F%2F+Hint%3A+The+declaration+on+line+4+is+missing+a+keyword+that+is+needed+in+Rust%0A%2F%2F+to+create+a+new+variable+binding.%0A)
- ["variables2.rs"](http://play.rust-lang.org/?code=%2F%2F+Make+me+compile%21%0A%0Afn+main%28%29+%7B%0A++++let+x%3B%0A++++if+x+%3D%3D+10+%7B%0A++++++++println%21%28%22Ten%21%22%29%3B%0A++++%7D+else+%7B%0A++++++++println%21%28%22Not+ten%21%22%29%3B%0A++++%7D%0A%7D%0A) - ["variables2.rs"](http://play.rust-lang.org/?code=%2F%2F+Make+me+compile%21+Scroll+down+for+hints+%3A%29%0A%0Afn+main%28%29+%7B%0A++++let+x%3B%0A++++if+x+%3D%3D+10+%7B%0A++++++++println%21%28%22Ten%21%22%29%3B%0A++++%7D+else+%7B%0A++++++++println%21%28%22Not+ten%21%22%29%3B%0A++++%7D%0A%7D%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%2F%2F+The+compiler+message+is+saying+that+Rust+cannot+infer+the+type+that+the%0A%2F%2F+variable+binding+%60x%60+has+with+what+is+given+here.%0A%2F%2F+What+happens+if+you+annotate+line+4+with+a+type+annotation%3F%0A%2F%2F+What+if+you+give+x+a+value%3F%0A%2F%2F+What+if+you+do+both%3F%0A%2F%2F+What+type+should+x+be%2C+anyway%3F%0A%2F%2F+What+if+x+is+the+same+type+as+10%3F+What+if+it%27s+a+different+type%3F%0A)
- ["variables3.rs"](http://play.rust-lang.org/?code=%2F%2F+Make+me+compile%21%0A%0Afn+main%28%29+%7B%0A++++let+x+%3D+3%3B%0A++++println%21%28%22Number+%7B%7D%22%2C+x%29%3B%0A++++x+%3D+5%3B%0A++++println%21%28%22Number+%7B%7D%22%2C+x%29%3B%0A%7D%0A) - ["variables3.rs"](http://play.rust-lang.org/?code=%2F%2F+Make+me+compile%21+Scroll+down+for+hints+%3A%29%0A%0Afn+main%28%29+%7B%0A++++let+x+%3D+3%3B%0A++++println%21%28%22Number+%7B%7D%22%2C+x%29%3B%0A++++x+%3D+5%3B%0A++++println%21%28%22Number+%7B%7D%22%2C+x%29%3B%0A%7D%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%2F%2F+In+Rust%2C+variable+bindings+are+immutable+by+default.+But+here+we%27re+trying%0A%2F%2F+to+reassign+a+different+value+to+x%21+There%27s+a+keyword+we+can+use+to+make%0A%2F%2F+a+variable+binding+mutable+instead.%0A)
- ["variables4.rs"](http://play.rust-lang.org/?code=%2F%2F+Make+me+compile%21%0A%0Afn+main%28%29+%7B%0A++++let+x%3A+i32%3B%0A++++println%21%28%22Number+%7B%7D%22%2C+x%29%3B%0A%7D%0A) - ["variables4.rs"](http://play.rust-lang.org/?code=%2F%2F+Make+me+compile%21+Scroll+down+for+hints+%3A%29%0A%0Afn+main%28%29+%7B%0A++++let+x%3A+i32%3B%0A++++println%21%28%22Number+%7B%7D%22%2C+x%29%3B%0A%7D%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%2F%2F+Oops%21+In+this+exercise%2C+we+have+a+variable+binding+that+we%27ve+created+on%0A%2F%2F+line+4%2C+and+we%27re+trying+to+use+it+on+line+5%2C+but+we+haven%27t+given+it+a%0A%2F%2F+value.+We+can%27t+print+out+something+that+isn%27t+there%3B+try+giving+x+a+value%21%0A%2F%2F+This+is+an+error+that+can+cause+bugs+that%27s+very+easy+to+make+in+any%0A%2F%2F+programming+language+--+thankfully+the+Rust+compiler+has+caught+this+for+us%21%0A)
### Uncategorized ### Uncategorized

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@ -1,6 +1,41 @@
// Make me compile! // Make me compile! Scroll down for hints :)
fn main() { fn main() {
x = 5; x = 5;
println!("x has the value {}", x); println!("x has the value {}", x);
} }
// Hint: The declaration on line 4 is missing a keyword that is needed in Rust
// to create a new variable binding.

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@ -1,4 +1,4 @@
// Make me compile! // Make me compile! Scroll down for hints :)
fn main() { fn main() {
let x; let x;
@ -8,3 +8,39 @@ fn main() {
println!("Not ten!"); println!("Not ten!");
} }
} }
// The compiler message is saying that Rust cannot infer the type that the
// variable binding `x` has with what is given here.
// What happens if you annotate line 4 with a type annotation?
// What if you give x a value?
// What if you do both?
// What type should x be, anyway?
// What if x is the same type as 10? What if it's a different type?

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@ -1,4 +1,4 @@
// Make me compile! // Make me compile! Scroll down for hints :)
fn main() { fn main() {
let x = 3; let x = 3;
@ -6,3 +6,37 @@ fn main() {
x = 5; x = 5;
println!("Number {}", x); println!("Number {}", x);
} }
// In Rust, variable bindings are immutable by default. But here we're trying
// to reassign a different value to x! There's a keyword we can use to make
// a variable binding mutable instead.

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@ -1,6 +1,44 @@
// Make me compile! // Make me compile! Scroll down for hints :)
fn main() { fn main() {
let x: i32; let x: i32;
println!("Number {}", x); println!("Number {}", x);
} }
// Oops! In this exercise, we have a variable binding that we've created on
// line 4, and we're trying to use it on line 5, but we haven't given it a
// value. We can't print out something that isn't there; try giving x a value!
// This is an error that can cause bugs that's very easy to make in any
// programming language -- thankfully the Rust compiler has caught this for us!