Chapter review: Hello

The program prints: Chatterbox v0.1 The first line inside main starts with //, so the whole line is a comment and the compiler never sees that old banner. On the next line, everything after // is a comment too, so the banner is a note for people, not text to print. Revisit lesson 1.3 if either surprised you.

It does not compile: E0061. banner promises two parameters, a bot and a version, and the call gives it one. A call has to match the function's first line exactly, one argument per parameter, so the compiler stops with E0061 and says which argument is missing. That contract is lesson 1.6.

error[E0061]: this function takes 2 arguments but 1 argument was supplied
 --> src/main.rs:6:20
  |
6 |     println!("{}", banner("Chatterbox"));
  |                    ^^^^^^-------------- argument #2 of type `&str` is missing
  |
note: function defined here
 --> src/main.rs:1:4
  |
1 | fn banner(bot: &str, version: &str) -> String {
  |    ^^^^^^            -------------
help: provide the argument
  |
6 |     println!("{}", banner("Chatterbox", /* &str */));
  |                                       ++++++++++++

The program prints: Sam sent 3 messages and 12 words The holes are filled left to right with the values after the comma. 1 + 2 and 3 * 4 are not text, they are sums, so Rust works each one out first and prints the result. Only what is inside the quotes is printed as it is written (lesson 1.3).

It does not compile: E0425. The parameter is called name, but the body asks for nmae. The compiler matches names letter by letter and nothing in the program is called nmae, so it stops with E0425, "cannot find value". The help line even suggests the parameter it probably meant. Lesson 1.5 takes this message apart.

error[E0425]: cannot find value `nmae` in this scope
 --> src/main.rs:2:39
  |
2 |     format!("Hi {}! I'm Chatterbox.", nmae)
  |                                       ^^^^
  |
help: a local variable with a similar name exists
  |
2 -     format!("Hi {}! I'm Chatterbox.", nmae)
2 +     format!("Hi {}! I'm Chatterbox.", name)
  |

The program prints: Chatterbox v0.1 Defining a function only writes the recipe down; nothing runs until it is called. The program starts in main, and main calls banner() first, so the banner is the first line, wherever the functions sit in the file. Lessons 1.1 and 1.6 both lean on this.

It does not compile: E0308. The last line has no semicolon, so its value is what banner hands back. But println! puts text on the screen and produces nothing, written (), while the arrow promised a String. Expected String, found (): E0308. Building the text with format! is what fits that promise (lessons 1.5 and 1.6).

error[E0308]: mismatched types
 --> src/main.rs:2:5
  |
2 |     println!("Chatterbox v0.1")
  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `String`, found `()`

It compiles and runs. It compiles and prints Chatterbox v0.1 | Hi Ada!. The compiler reads the whole file before it complains about a name, so functions written below main are found. And a call like banner() is an expression, so it can fill a hole inside another function's format!. Revisit lesson 1.6 if you expected E0425.