What is Control Flow in Rust?
Description
- A control flow is an order in which the piece of program is executed.
- In control flow we have the following expressions:
- If expression
- Else expression
- Else if expression
If Expression:
- If expression permits to branch your code to any condition.
- If the condition is true then the program in if block will be executed.
- if when an expression is not true then the program would be passed to further blocks of else if expressions or else expression.
- The curly brackets which define the program blocks are called arms.
Else Expression:
- Else expression provides the program an alternative block of code to execute when the condition introduced in if block evaluates to false.
- Else expression comes at last.
Example
fn main() {
let number = 3;
if number <5 {
println!("condition was
true");
} else {
println!("condition was
false");
}
}
Result:
Condition was true
Example
fn main() {
let number = 7;
if number <5 {
println!("condition was true");
} else {
println!("condition was
false");
}
}
Result:
Condition was false
Note:
- The condition introduced in if expression and else if expression should be bool type (true or false). Otherwise, the program will not run.
- Rust will not automatically try to convert non-Boolean types to a Boolean.
Example
fn main() {
let number = 3;
if number {
println!("number was
something other than zero");
}
}
Result:
A compile-time error occurs.
Note:
Here Rust will give an error because instead of giving a bool condition we have placed an integer in condition.
Else If Expression:
- Else if the expression is used to introduce multiple conditions.
- This expression is always situated between if expression an else expression.
Example
fn main() {
let number = 6;
if number % 4 == 0 {
println!("number is divisible by 4");
} else if number % 3 == 0 {
println!("number is divisible by 3");
} else if number % 2 == 0 {
println!("number is divisible by 2");
} else {
println!("number is not divisible by
4, 3, or 2");
} }
Result:
The number is divisible by 4
Note:
- In the above example, there are two true conditions but Rust print the block of the first true condition.
- This means Rust only executes the block of the first true condition.
Using if inlet statement
- We can use if expression to store different values depending upon the condition in a variable using let statement, as mentioned in next example.
Example
fn main() {
let condition = true;
let number = if condition {
5 // (no semicolon means
expression)
} else {
6 // (no semicolon means
expression)
};
println!("The value of number is:
{ }", number);
}
Note:
A value of 5 will be stored in the number variable.
Example
fn main() {
let condition = true;
let number = if condition {
5
} else {
"six"
};
println!("The value of number
is: {}", number);
}
Result:
Compile error will occur
Note:
Expression types are mismatched in each arm, hence an error will occur.
