[易学易懂系列|rustlang语言|零基础|快速入门|（9）|Control Flows流程控制]

[易学易懂系列|rustlang语言|零基础|快速入门|（9）]

有意思的基础知识

Control Flows

---

我们今天再来看看流程控制。

条件控制 if-else if -else:

/ Simplest Example
let team_size = 7;
if team_size < 5 {
    println!("Small");
} else if team_size < 10 {
    println!("Medium");
} else {
    println!("Large");
}
​
// partially refactored code
let team_size = 7;
let team_size_in_text;
if team_size < 5 {
    team_size_in_text = "Small";
} else if team_size < 10 {
    team_size_in_text = "Medium";
} else {
    team_size_in_text = "Large";
}
println!("Current team size : {}", team_size_in_text);
​
//optimistic code
let team_size = 7;
let team_size_in_text = if team_size < 5 {
    "Small" //⭐️no ;
} else if team_size < 10 {
    "Medium"
} else {
    "Large"
};
println!("Current team size : {}", team_size_in_text);
​
​
let is_below_eighteen = if team_size < 18 { true } else { false };

模式匹配 match ：

let tshirt_width = 20;
let tshirt_size = match tshirt_width {
    16 => "S", // check 16
    17 | 18 => "M", // check 17 and 18
    19 ... 21 => "L", // check from 19 to 21 (19,20,21)
    22 => "XL",
    _ => "Not Available",
};
println!("{}", tshirt_size); // L
​
​
let is_allowed = false;
let list_type = match is_allowed {
    true => "Full",
    false => "Restricted"
    // no default/ _ condition can be skipped
    // Because data type of is_allowed is boolean and all possibilities checked on conditions
};
println!("{}", list_type); // Restricted
​
​
let marks_paper_a: u8 = 25;
let marks_paper_b: u8 = 30;
let output = match (marks_paper_a, marks_paper_b) {
    (50, 50) => "Full marks for both papers",
    (50, _) => "Full marks for paper A",
    (_, 50) => "Full marks for paper B",
    (x, y) if x > 25 && y > 25 => "Good",
    (_, _) => "Work hard"
};
println!("{}", output); // Work hard

while:

let mut a = 1;
while a <= 10 {
    println!("Current value : {}", a);
    a += 1; //no ++ or -- on Rust
}
​
// Usage of break and continue
let mut b = 0;
while b < 5 {
    if b == 0 {
        println!("Skip value : {}", b);
        b += 1;
        continue;
    } else if b == 2 {
        println!("Break At : {}", b);
        break;
    }
    println!("Current value : {}", b);
    b += 1;
}
​
// Outer break
let mut c1 = 1;
'outer_while: while c1 < 6 { //set label outer_while
    let mut c2 = 1;
    'inner_while: while c2 < 6 {
        println!("Current Value : [{}][{}]", c1, c2);
        if c1 == 2 && c2 == 2 { break 'outer_while; } //kill outer_while
        c2 += 1;
    }
    c1 += 1;
}

loop

loop {
    println!("Loop forever!");
}
​
// Usage of break and continue
let mut a = 0;
loop {
    if a == 0 {
        println!("Skip Value : {}", a);
        a += 1;
        continue;
    } else if a == 2 {
        println!("Break At : {}", a);
        break;
    }
    println!("Current Value : {}", a);
    a += 1;
}
​
// Outer break
let mut b1 = 1;
'outer_loop: loop { //set label outer_loop
  let mut b2 = 1;
  'inner_loop: loop {
    println!("Current Value : [{}][{}]", b1, b2);
    if b1 == 2 && b2 == 2 {
        break 'outer_loop; // kill outer_loop
    } else if b2 == 5 {
        break;
    }
    b2 += 1;
  }
  b1 += 1;
}

for

for a in 0..10 { //(a = o; a <10; a++) // 0 to 10(exclusive)
  println!("Current value : {}", a);
}
​
// Usage of break and continue
for b in 0..6 {
  if b == 0 {
    println!("Skip Value : {}", b);
    continue;
  } else if b == 2 {
    println!("Break At : {}", b);
    break;
  }
  println!("Current value : {}", b);
}
​
// Outer break
'outer_for: for c1 in 1..6 { //set label outer_for
  'inner_for: for c2 in 1..6 {
    println!("Current Value : [{}][{}]", c1, c2);
    if c1 == 2 && c2 == 2 { break 'outer_for; } //kill outer_for
  }
}
​
​
// Working with arrays/vectors
let group : [&str; 4] = ["Mark", "Larry", "Bill", "Steve"];
​
for n in 0..group.len() { //group.len() = 4 -> 0..4 👎 check group.len()on each iteration
  println!("Current Person : {}", group[n]);
}
​
for person in group.iter() { //👍 group.iter() turn the array into a simple iterator
  println!("Current Person : {}", person);
}

以上，希望对你有用。

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参考文章： https://learning-rust.github.io/docs/a10.control_flows.html