Start with the idea
Most Rust syntax is expression-oriented. The last expression in a block becomes its value when it has no semicolon. Adding a semicolon changes that expression into a statement and the block then produces (), the unit value. This one rule explains function returns, if branches, match arms, and scoped calculations.
Read the braces as a small computation with its own scope. In the example, base exists inside the block, then base * 2 is the final expression. The whole block evaluates to 14, which is assigned to score. There is no separate return statement because the final expression supplies the value. If you put a semicolon after base * 2, that line becomes a statement and the block's value becomes (), the unit type. A variable expecting an integer can no longer receive it.
This rule appears repeatedly in Rust.
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