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| -rw-r--r-- | src/doc/book/src/ch03-03-how-functions-work.md | 22 |
1 files changed, 12 insertions, 10 deletions
diff --git a/src/doc/book/src/ch03-03-how-functions-work.md b/src/doc/book/src/ch03-03-how-functions-work.md index c698853ce..2b59f0cd4 100644 --- a/src/doc/book/src/ch03-03-how-functions-work.md +++ b/src/doc/book/src/ch03-03-how-functions-work.md @@ -35,8 +35,8 @@ should see the following output: ``` The lines execute in the order in which they appear in the `main` function. -First, the “Hello, world!” message prints, and then `another_function` is -called and its message is printed. +First the “Hello, world!” message prints, and then `another_function` is called +and its message is printed. ### Parameters @@ -108,8 +108,9 @@ understand. Other languages don’t have the same distinctions, so let’s look what statements and expressions are and how their differences affect the bodies of functions. -*Statements* are instructions that perform some action and do not return a -value. *Expressions* evaluate to a resulting value. Let’s look at some examples. +* **Statements** are instructions that perform some action and do not return + a value. +* **Expressions** evaluate to a resultant value. Let’s look at some examples. We’ve actually already used statements and expressions. Creating a variable and assigning a value to it with the `let` keyword is a statement. In Listing 3-1, @@ -172,10 +173,11 @@ This expression: is a block that, in this case, evaluates to `4`. That value gets bound to `y` as part of the `let` statement. Note that the `x + 1` line doesn’t have a -semicolon at the end, unlike most of the lines you’ve seen so far. Expressions -do not include ending semicolons. If you add a semicolon to the end of an -expression, you turn it into a statement, and it will then not return a value. -Keep this in mind as you explore function return values and expressions next. +semicolon at the end, which is unlike most of the lines you’ve seen so far. +Expressions do not include ending semicolons. If you add a semicolon to the end +of an expression, you turn it into a statement, and it will then not return a +value. Keep this in mind as you explore function return values and expressions +next. ### Functions with Return Values @@ -226,7 +228,7 @@ Let’s look at another example: Running this code will print `The value of x is: 6`. But if we place a semicolon at the end of the line containing `x + 1`, changing it from an -expression to a statement, we’ll get an error. +expression to a statement, we’ll get an error: <span class="filename">Filename: src/main.rs</span> @@ -240,7 +242,7 @@ Compiling this code produces an error, as follows: {{#include ../listings/ch03-common-programming-concepts/no-listing-23-statements-dont-return-values/output.txt}} ``` -The main error message, “mismatched types,” reveals the core issue with this +The main error message, `mismatched types`, reveals the core issue with this code. The definition of the function `plus_one` says that it will return an `i32`, but statements don’t evaluate to a value, which is expressed by `()`, the unit type. Therefore, nothing is returned, which contradicts the function |