refactor: exercises to manage of None and Errors

- Use of Result and Option 
- Use of Some and None
- Use of Ok and Err
- Use of match
- Use of unwrap

match-some-err-options-results/.gitignore

@@ -0,0 +1,2 @@
+/target
+**/*.rs.bk

match-some-err-options-results/Cargo.toml

@@ -0,0 +1,7 @@
+[package]
+name = "match-some-err-options-results"
+version = "0.1.0"
+authors = ["Stivenson Rincón <stivenson.rpm@gmail.com>"]
+edition = "2018"
+
+[dependencies]

match-some-err-options-results/src/main.rs

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+// Return result or None
+fn get_slice_or_possible_none(phrase: String) -> Option<String> {
+    if &phrase == "" {
+        None
+    } else {
+        let first_letters = &phrase[0..2];
+        Some(first_letters.to_string())
+    }
+}
+
+// Return result or error
+fn get_div_or_possible_error(operators: (u32, u32)) -> Result<u32, &'static str>{
+    if operators.1 == 0 {
+        Err("Second operator is zero")
+    } else {
+        Ok(operators.0 / operators.1)
+    }
+}
+
+fn main() {
+
+    // Omit check of possible None
+    println!("First Letters of Empty string: {:?}",get_slice_or_possible_none("hi! Stivenson".to_string()).unwrap());
+    println!("First Letters of string: {:?}",get_slice_or_possible_none("".to_string()));
+
+
+
+    // Manage possible "None" or successful
+    let res = get_slice_or_possible_none("hi! Stivenson".to_string());
+    match res {
+        Some(letters) => {
+            println!("First Letters of string: {:?}", letters);
+        },
+        None => {
+            println!("Empty String");
+        }
+    }
+    let res = get_slice_or_possible_none("".to_string()); // overwriting to res
+    match res {
+        Some(letters) => {
+            println!("First Letters of string: {:?}", letters);
+        },
+        None => {
+            println!("Empty String");
+        }
+    }
+
+
+    // Manage possible error or successful
+    let possible_error = get_div_or_possible_error((10,2));
+    match possible_error {
+        Ok(result_div) => {
+            println!("Div without error: {:?}", result_div);
+        },
+        Err(message) => {
+            println!("Div with error: {:?}", message);
+        }
+    }
+    let possible_error = get_div_or_possible_error((10,0)); // overwriting to possible_error
+    match possible_error {
+        Ok(result_div) => {
+            println!("Div without error: {:?}", result_div);
+        },
+        Err(message) => {
+            println!("Div with error: {:?}", message);
+        }
+    }
+}