// if1.rs
pub fn bigger(a: i32, b: i32) -> i32 {
// Complete this function to return the bigger number!
// Do not use:
// - another function call
// - additional variables
// Execute `rustlings hint if1` for hints
}
// Don't mind this for now :)
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn ten_is_bigger_than_eight() {
assert_eq!(10, bigger(10, 8));
}
#[test]
fn fortytwo_is_bigger_than_thirtytwo() {
assert_eq!(42, bigger(32, 42));
}
}
这里大家能注意到fn前多了一个pub。Rust中有两种简单的访问权：公共(public)和私有(private)。这个pub就代表公共。后续会详细讲解。
还有下面的mod。Rust中的组织单位是模块(Module)，#[cfg(test)]是模块的对应注解。这些先略过，我们主要关注目前的具体问题。
Rust的if表达式和C/C++差不多。只是多注意返回值就可以了。assert_eq!函数将bigger的返回值和10进行比较，所以if花括号里的表达式也是i32。
因为if是个表达式，它有返回值，所以可以放在let的右侧，绑定在变量上。实例如下：
fn main() {
let condition = true;
let number = if condition {
5
} else {
6
};
println!("The value of number is: {}", number);
}
pub fn bigger(a: i32, b: i32) -> i32 {
// Complete this function to return the bigger number!
// Do not use:
// - another function call
// - additional variables
// Execute `rustlings hint if1` for hints
if a > b {
a
}
else{
b
}
}
需要注意的是if-else分支必须完备，如果单只有一个if，其他分支未覆盖全的话，编译器会认定有不走if的情况，从而报错。这个在C中有可能是警告。因为在C中如果返回值是整数或指针类型，就会默认返回0并抛出警告，若不能强制返回0的话才会报错。
Rust编译器 yyds
// if2.rs
// Step 1: Make me compile!
// Step 2: Get the bar_for_fuzz and default_to_baz tests passing!
// Execute the command `rustlings hint if2` if you want a hint :)
pub fn fizz_if_foo(fizzish: &str) -> &str {
if fizzish == "fizz" {
"foo"
} else {
1
}
}
// No test changes needed!
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn foo_for_fizz() {
assert_eq!(fizz_if_foo("fizz"), "foo")
}
#[test]
fn bar_for_fuzz() {
assert_eq!(fizz_if_foo("fuzz"), "bar")
}
#[test]
fn default_to_baz() {
assert_eq!(fizz_if_foo("literally anything"), "baz")
}
}
if2相较于if1就是多了分支，无需赘述。
pub fn fizz_if_foo(fizzish: &str) -> &str {
if fizzish == "fizz" {
"foo"
} else if fizzish == "fuzz" {
"bar"
} else if fizzish == "literally anything" {
"baz"
} else {
"1"
}
}
// quiz1.rs
// This is a quiz for the following sections:
// - Variables
// - Functions
// Mary is buying apples. One apple usually costs 2 Rustbucks, but if you buy
// more than 40 at once, each apple only costs 1! Write a function that calculates
// the price of an order of apples given the order amount. No hints this time!
// Put your function here!
// fn ..... {
// Don't modify this function!
#[test]
fn verify_test() {
let price1 = calculate_apple_price(35);
let price2 = calculate_apple_price(40);
let price3 = calculate_apple_price(65);
assert_eq!(70, price1);
assert_eq!(80, price2);
assert_eq!(65, price3);
}
这个程序逻辑很简单，就是对购买数量进行一个if判断，返回值不同而已。
pub fn calculate_apple_price(prices:i32) -> i32 {
if prices < 40 { 2 * prices }
else { prices }
}