Fillng out some exercise program thing

.gitignore

@@ -2,7 +2,5 @@
 *.log
 *env
 .dep
-/guessing_game/target/
-/hello_cargo/target/
+**/target/
 /hello_world/main
-/scarytxt/target/

variables/Cargo.lock

@@ -0,0 +1,5 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+[[package]]
+name = "variables"
+version = "0.1.0"

variables/Cargo.toml

@@ -0,0 +1,9 @@
+[package]
+name = "variables"
+version = "0.1.0"
+authors = ["Dan Buch <dan@meatballhat.com>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

variables/src/main.rs

@@ -0,0 +1,72 @@
+use std::env;
+use std::process;
+
+fn main() {
+    let mut command = String::new();
+    let mut command_args = Vec::<String>::new();
+    for (i, arg) in env::args().enumerate() {
+        match i {
+            0 => continue,
+            1 => {
+                command = arg;
+                continue;
+            }
+            _ => command_args.push(arg.as_str().to_string()),
+        }
+    }
+
+    match command.as_str() {
+        "tc" => {
+            if command_args.len() < 1 {
+                println!("ERROR: missing a value to convert");
+                process::exit(1);
+            }
+            temp_convert(command_args[0].as_str().to_string())
+        }
+        "rx" => redefine_x(),
+        "help" | _ => show_help(),
+    }
+}
+
+fn show_help() {
+    println!("Usage: variables <command> [command_args]");
+    println!();
+    println!("The value for <command> may be one of:");
+    println!("  tc - convert temperatures between Fahrenheit and Celsius");
+    println!("  rx - redefine x");
+    println!();
+}
+
+fn redefine_x() {
+    let mut x = 5;
+    println!("The value of x is: {}", x);
+    x = 6;
+    println!("The value of x is: {}", x);
+}
+
+fn temp_convert(to_convert: String) {
+    let to_convert = to_convert.to_lowercase();
+    if to_convert.ends_with("c") {
+        let c: f32 = to_convert
+            .trim_end_matches('c')
+            .parse()
+            .expect("failed to parse temperature");
+        println!("{}F", temp_convert_c2f(c));
+    } else if to_convert.ends_with("f") {
+        let f: f32 = to_convert
+            .trim_end_matches('f')
+            .parse()
+            .expect("failed to parse temperature");
+        println!("{}C", temp_convert_f2c(f));
+    } else {
+        println!("What are we supposed to do to {:?}?", to_convert);
+    }
+}
+
+fn temp_convert_c2f(c: f32) -> f32 {
+    (c * (9.0 / 5.0)) + 32.0
+}
+
+fn temp_convert_f2c(f: f32) -> f32 {
+    (f - 32.0) * (5.0 / 9.0)
+}