1.用三种方式生成内容为1、2、3的可变数组
NSMutableArray* arr = [NSMutableArray arrayWithObjects:@1,@2,@3,nil];
NSMutableArray* arr = [@[@1,@2,@3] mutableCopy];
NSMutableArray* arr = [NSMutableArray arrayWithArray:@[@1,@2,@3]];
NSMutableArray* arr = [NSMutableArray arrayWithObjects:@1,@2,@3,nil];
NSMutableArray* arr = [@[@1,@2,@3] mutableCopy];
NSMutableArray* arr = [NSMutableArray arrayWithArray:@[@1,@2,@3]];