Objective C - Pass by value and pass by reference
===

First of all sorry for this simple question. But I need to understand how this happens. Output is below. I thought it should be "upper case string".

value after changed : UPPER CASE STRING

    -(void) test
    {
         NSString *stringVar = @"UPPER CASE STRING";
         [self changeString:stringVar];
         NSLog(@"value after changed : %@", stringVar);
    }
    
    -(void) changeString:(NSString*)string
    {
         string = [string lowercaseString];
    }