Each example is added in Cargo.toml as below.
[[bin]]
name = "function_for"
path = "src/function_for/main.rs"
Cargo can build and run each example as below.
gurugio@AL01945427:~/my-rust-book$ cargo build --bin function_for
Compiling my-rust-book v0.1.0 (/home/gurugio/my-rust-book)
Finished dev [unoptimized + debuginfo] target(s) in 0.17s
gurugio@AL01945427:~/my-rust-book$ cargo run --bin function_for
Finished dev [unoptimized + debuginfo] target(s) in 0.00s
Running `target/debug/function_for`
Hello, function_for!
3 - Fizz
5 - Buzz
6 - Fizz
9 - Fizz
10 - Buzz