Objective-C数组NSArray与可变数组NSMutableArray使用

NSArray *arr = [[NSArray alloc] initWithObjects:@"Hello",@"World",@"Nice", nil];
    for (int i=0; i<arr.count; i++) {
        NSLog(@"->%@\n",[arr objectAtIndex:i]);
    }
    for (id s in arr.objectEnumerator) {
        NSLog(@"==>%@",s);
    }
    for (id s in arr.reverseObjectEnumerator) {
        NSLog(@"==>%@",s);
    }
    int nums[] = {1,2,3,4,5,6,7,8,9};
    
    NSArray *arr3 = [NSArray arrayWithObjects:@"1",@"2",@"3",@"4",@"5", nil];
    NSArray *arr2 = [[NSArray alloc] initWithArray:arr];
    NSArray *arr4 = [arr3 subarrayWithRange:NSMakeRange(2, 3)];
    NSLog(@"%@,%@,%@",arr4,arr4.firstObject,arr4.lastObject);
    [arr writeToFile:@"test.txt" atomically:YES];
    
    //从已有Array创建新Array
    NSMutableArray *marr = [[NSMutableArray alloc] initWithArray:arr4];
    NSLog(@"%@",marr);
    //遍历数组,向Array添加元素
    for (int i=0; i<9; i++) {
        id x = [[NSString alloc] initWithFormat:@"%d",i];
        [marr addObject:x];
    }
    NSLog(@"%@",marr);
    [marr removeObjectAtIndex:2];//删除5
    [marr removeLastObject];//删除8
    [marr removeObjectsInRange:NSMakeRange(3, 4)];//从第3个开始删除4个元素 删除1,2,3,4
    for (id x in marr.objectEnumerator) {
        NSLog(@"%@",x);
    }
    
    NSArray *arr6=@[@1,@2,@3,@4,@5];
    [marr addObjectsFromArray:arr6];
    NSLog(@"%@",marr);