Control flow constructs empower programmers to steer the execution of their code. This guide delves into the core tools that Rust provides for making decisions and iterating through tasks.
Conditional Statements: If, Else If, Else
Conditional statements are the bedrock of decision-making in any programming language. In Rust, they are both powerful and flexible:
If Statement
The if statement evaluates a condition and executes a code block if the condition is true.
let num = 10;
if num > 0 {
println!("Number is positive.");
}
Else If Clause
The else if clause allows you to test multiple conditions sequentially.
let temperature = 25;
if temperature > 30 {
println!("It's hot outside!");
} else if temperature > 20 {
println!("It's warm.");
} else {
println!("It's chilly.");
}
Else Clause
The else clause provides a default action when none of the preceding conditions are met.
let is_raining = true;
if is_raining {
println!("Don't forget an umbrella!");
} else {
println!("Enjoy the weather!");
}
Matching and Pattern Matching
Rust's match statement takes control flow to the next level by enabling pattern matching:
let grade = "B";
match grade {
"A" => println!("Excellent!"),
"B" | "C" => println!("Good."),
"D" => println!("Passing."),
_ => println!("Not a valid grade."),
}
In this example, the match statement compares the value of grade against various patterns and executes the corresponding code block for the first matching pattern. The _ serves as a catch-all for patterns not explicitly listed.
Looping with While and For
Loops allow repetitive tasks to be performed efficiently. Rust offers two fundamental loop constructs:
While Loop
The while loop continues to execute a block of code as long as a given condition remains true.
let mut count = 0;
while count < 5 {
println!("Count: {}", count);
count += 1;
}
For Loop
The for loop iterates over a range, collection, or data that implements the Iterator trait.
for number in 1..=5 {
println!("Number: {}", number);
}
In this example, the for loop iterates through the range from 1 to 5 (inclusive) and prints each number.
In the upcoming sections, we'll delve into these control flow constructs with more detailed examples and insights, allowing you to harness their capabilities to craft efficient and expressive Rust programs.
