Objective-C字符串类、数组类

        NSString* str1 = @"dancer";
        NSString* str2 = [[NSString alloc] initWithFormat:@"%d beijing",1949];
        NSString* str3 = [NSString stringWithFormat:@"%ld beijing",1948];
        NSUInteger len = str1.length;
        //计算长度
        //注：一个汉字一个长度
        NSLog(@"%lu",len);
        //比较相等
        BOOL result = [str1 isEqualTo:str2];
        if(result){
            NSLog(@"相等");
        }else{
            NSLog(@"不相等");
        }

        //NSMutableArray可变数组
        NSMutableArray* array = [[NSMutableArray alloc]init];
        //数组可以存放任意类型的对象
        //增删改查
        [array addObject:@"obj1"];
        //通过对象删除
        [array removeObject:@"obj1"];
        //通过索引删除
        [array removeObjectAtIndex:0];
        //访问数组元素
        NSString* item1 =  array[0];