Update README and add Fahrenheit to Celsius conversion function

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "rfcalc"
-version = "0.3.3"
+version = "0.4.0"
 edition = "2021"
 authors = ["R4 Cheng <[email protected]>"]
 license = "MIT"

README.md

@@ -9,9 +9,12 @@
 
 ## Usage
 
+E.g.
+
 - `rfcalc factorial <NUM>`: Calculate the factorial of a number (max: 20)
 - `rfcalc hw <NUM>`: Calculate the Hamming weight of a binary number
 - `rfcalc c <N> <K>`: Calculate the combination of `N` choose `K`
+- `rfcalc fc <NUM>`: Convert degree from Fahrenheit to Celsius
 
 ### `rfcalc bytes <expression to calculate>`
 

src/calc.rs

@@ -27,6 +27,10 @@ pub fn calc_combination(n: u64, k: u64) -> u64 {
     numerator / denominator
 }
 
+pub fn fahrenheit_to_celsius(f: f64) -> f64 {
+    (f - 32.0) * 5.0 / 9.0
+}
+
 /// B: byte
 #[derive(PartialEq, PartialOrd)]
 enum ByteUnit {

src/main.rs

@@ -18,6 +18,8 @@ enum Functions {
     C { n: u64, k: u64 },
     /// Calculate the difference in bytes by how many times
     Bytes { expression: String },
+    /// Fahrenheit to Celsius
+    FC { f: f64 },
 }
 
 fn main() {
@@ -42,5 +44,9 @@ fn main() {
             let bytes = calc::devide_bytes(expression);
             println!("{}", bytes);
         }
+        Functions::FC { f } => {
+            let c = calc::fahrenheit_to_celsius(*f);
+            println!("{}", c);
+        }
     }
 }