done with basic calc

exercises/02_basic_calculator/06_while/src/lib.rs

@@ -4,7 +4,16 @@ pub fn factorial(n: u32) -> u32 {
     // interprets as "I'll get back to this later", thus
     // suppressing type errors.
     // It panics at runtime.
-    todo!()
+    if n == 0 || n == 1 {
+        return 1;
+    }
+    let mut i = 1;
+    let mut prod = 1;
+    while i <= n {
+        prod = prod * i;
+        i = i + 1;
+    }
+    return prod;
 }
 
 #[cfg(test)]