# 递归与栈

理解递归之前想要理解函数。

只有函数才能递归。

## 函数

关于计算机里的函数

```c
int main() {
    for (int i = 0; i < 100; i++) {
        cout << i << endl;
    }
}
```

数学里的函数

$$y = x^2 + 2x + 1 = (x + 1)^2$$

数学上的函数和计算机里的函数是有区别的，计算机里的函数要多一些东西东西的。


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