Rust Platform

🎯 In Python, every variable is mutable by default:

total = 0
for i in range(4):
    total += i
# total is now 6

No special syntax needed — you just reassign. Rust takes the opposite approach: variables are immutable by default. If you want to change a value, you must explicitly opt in with mut:

let counter = 1;       // immutable — can't change this
let mut counter = 1;   // mutable — now you can

This isn't a restriction for the sake of it. Immutability by default means the compiler catches accidental mutations — a class of bug that Python can't detect until runtime.

Loops in Rust

Rust's for loop works over ranges and iterators:

for _ in 0..5 {
    // runs 5 times (0, 1, 2, 3, 4)
}

0..5 is a half-open range (excludes 5), like Python's range(5). The _ means "I don't need the loop variable."

Your Task

Implement the double_counter function:

• Create a mutable counter variable starting at 1
• Double it 5 times in a loop using a range
• Return the final result (should be 32)

Don't hardcode the return value — use a mutable variable and a loop.

Example

assert_eq!(double_counter(), 32);

Further Reading

• The Rust Book — Variables and Mutability — let, let mut, and const
• The Rust Book — Loops — for, while, and loop