熟悉OC--3：多用字面量语法，少用与之等价的方法

NSString *str = @"string";

NSNumber *num = @12;
NSNumber *floatNum = @12.5f;
NSNumber *boolNum = @YES;
    
NSArray *arr = @[@"obj1",@"obj2"];
NSDictionary *dic = @{
                      @"name":@"MM",
                      @"age":@12
                      };