feat: add array4.rs exercise

exercises/array/array4.rs

@@ -0,0 +1,27 @@
+
+// array4.rs
+//
+// Here is the code for how the array learns
+
+// I AM NOT DONE
+
+
+
+fn main(){
+    // define  arrays a 
+let a =[1,2,3,4,5];
+     println!("please enter an array index.");
+let mut  index = String::new();
+     std::io::stdin()
+             .read_line(&mut index)
+             .expect("Fail to read line");
+let index :usize =index
+             .trim()
+             .parse()
+             .expect("index entered was not a number");
+     
+let element = a[index];
+     println!("The value of is {}  element : {}",index,element);
+     
+ }
+