我正在制作一个简单的控制台程序,可以在摄氏温度和华氏温度之间转换。该程序多次接受用户输入,一次输入转换类型,一次输入转换值。当我运行程序时,它会编译并没有错误地运行,但是,它实际上并没有返回任何值。
这是程序:
use std::io;
// C to F: F = C*(9/5) + 32
// F to C: C = (F-32)*(5/9)
/**********Converts between Fahrenheit and Celsius*********/
fn main() -> () {
println!("Do you want to convert to Celsius or Fahrenheit? Input C or F");
let mut convert_type = String::new();
io::stdin()
.read_line(&mut convert_type)
.expect("Failed to conversion type.");
let t = String::from(convert_type);
println!("You want to convert to: {}", t);
println!("What temperature would you like to convert?");
let mut temp = String::new();
io::stdin()
.read_line(&mut temp)
.expect("Failed to read temperature.");
let temp: i32 = match temp.trim().parse() {
Ok(temp) => temp,
Err(_e) => -1,
};
if &t == "C" {
println!("{}", ctof(temp));
} else if &t == "F" {
println!("{}", ftoc(temp));
}
}
// Celsius to Fahrenheit
fn ctof(c: i32) -> i32 {
(c * (9 / 5)) + 32
}
//Fahrenheit to Celsius
fn ftoc(f: i32) -> i32 {
(f - 32) * (5 / 9)
}
以下是控制台的摘要,如您所见,它不输出转换:
cargo run --verbose
Compiling ftoc v0.1.0 (/Users/roberthayek/rustprojects/ftoc)
Running `rustc --crate-name ftoc src/main.rs --color always --crate-type bin --emit=dep-info,link -C debuginfo=2 -C metadata=8f02d379c2e5c97d -C extra-filename=-8f02d379c2e5c97d --out-dir /Users/roberthayek/rustprojects/ftoc/target/debug/deps -C incremental=/Users/roberthayek/rustprojects/ftoc/target/debug/incremental -L dependency=/Users/roberthayek/rustprojects/ftoc/target/debug/deps`
Finished dev [unoptimized + debuginfo] target(s) in 1.16s
Running `target/debug/ftoc`
Do you want to convert to Celsius or Fahrenheit? Input C or F
C
You want to convert to: C
What temperature would you like to convert?
0
答案 0 :(得分:12)
您应该养成处理所有案件的习惯,即使您没有想到。如果这样做,您将发现问题。所以代替这个:
if &t == "C" {
println!("{}", ctof(temp));
} else if &t == "F" {
println!("{}", ftoc(temp));
}
您可以这样写(您也可以使用没有if的final else分支,但匹配更具吸引力):
match t.as_str() {
"C" => println!("{}", ctof(temp)),
"F" => println!("{}", ftoc(temp)),
_ => println!("please enter C or F"),
}
运行程序时,您会发现t
似乎既不等于"C"
也不等于"F"
。希望可以通过调试打印来检查t
的值。
match t.as_str() {
"C" => println!("{}", ctof(temp)),
"F" => println!("{}", ftoc(temp)),
_ => println!("t = {:?}", t),
}
此时,您会看到t
的值不是"C"
,而是"C\n"
或"C\r\n"
。然后您会意识到read_line
并没有为您剥离字符串中的换行符。