added lower and stringchars examples

Author: BartMassey

README.md

@@ -39,3 +39,5 @@ in a controlled repository now.
 * `setimpl.rs`: example implementation of `HashSet` as `HashMap`
 * `rng/`: example use of `rand` crate
 * `charcast.rs`: character / number casting examples
+* `lower.rs`: boring character lowercase example
+* `stringchars.rs`: string ←→ chars conversion examples

charcast.rs

@@ -8,4 +8,5 @@ fn main() {
     println!("{:016x}", '🦀' as u64);
 
     println!("{}", 0x78u8 as char);
+    // println!("{}", 0x1f980u32 as char); // Nope.
 }

lower.rs

@@ -0,0 +1,4 @@
+fn main() {
+    let s: String = 'ß'.to_uppercase().collect();
+    println!("{}", s);
+}

stringchars.rs

@@ -0,0 +1,17 @@
+fn main() {
+    let s = "🦀hello";
+    println!("nbytes {}", s.len());
+    println!("nchar {}", s.chars().count());
+    println!("{}", s.chars().nth(0).unwrap());
+    let t: String = s.chars().take(5).collect();
+    println!("{}", t);
+    let u = s.as_bytes();
+    println!("{:02x?}", u);
+    let v = std::str::from_utf8(u).unwrap();
+    println!("{}", v);
+    let v = unsafe { std::str::from_utf8_unchecked(u) };
+    println!("{}", v);
+    let mut w = u.to_vec();
+    w[0] = 0;
+    println!("{}", unsafe { std::str::from_utf8_unchecked(&w) });
+}