c ++嵌套循环输出结果

Question

我想在屏幕上输出这个结果：

  

1
23
456
78910

怎么做？ 我试着写这段代码：

for (int line = 1; line <= 4; line++){
    int num = line;
    int i = 1;
    for (int x = 1; x <= line; x++){
        cout << num;
        num = num + i;
    }
    cout << endl;
}

但输出是：

  

1
23
345
4567

请帮助!!!

Answer 1

在num循环之外创建for并在写完后将其递增。

int num = 1;
for (int line = 1; line <= 4; line++){
    for (int x = 1; x <= line; x++){
        cout << num;
        ++num;
    }
    cout << endl;
}

Answer 2

int num = 1;
int i = 1;
for (int line = 1; line <= 4; line++){
    for (int x = 1; x <= line; x++){
        cout << num;
        num = num + i;
    }
    cout << endl;
}