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d84748 Qwas 2024-11-17 13:36:49 1 
# c++入门
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- `endl` 用于向流的末尾部位加入换行符
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- `cout` 代表显示器
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- `cout << x` 操作就相当于把x的值输出到显示器
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## 输入 Hello World
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```cpp
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# include<iostream>
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using namespace std;
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int main() {
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cout <<"Hello World!\n";
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}
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```
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## 输入输出
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```cpp
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#include <iostream>
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using namespace std;
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int main() {
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int a, b, result;
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cout << "please input two number:\n";
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cin >> a >> b;
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result = 3 * a - 2 * b + 1;
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cout << "result is " << result << endl;
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}
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```
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![](/cpp/c++%E5%85%A5%E9%97%A8/a/image-1731850280498.jpg)
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## 使用函数
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```cpp
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#include<iostream>
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#include<cmath>
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using namespace std;
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double max(double x, double y);
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int main() {
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double a, b, c;
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cout << "input two number:\n";
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cin >> a >> b;
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c = max(a, b);
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cout << "maximum=" << c << "\n";
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cout << "the squart of maximum=" << sqrt(c);
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}
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double max(double x, double y) {
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if (x > y)
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return x;
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else
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return y;
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}
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```
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![](/cpp/c++%E5%85%A5%E9%97%A8/a/image-1731850497554.jpg)
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## 函数定义包含函数声明
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```cpp
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#include<iostream>
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#include<cmath>
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using namespace std;
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double max(double x, double y) { // 既是函数定义又是函数声明
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if (x > y)
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return x;
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else
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return y;
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}
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int main() {
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double a, b, c;
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cout << "input two numbers:\n";
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cin >> a >> b;
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c = max(a, b);
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cout << "the squart of maximum=" << sqrt(c);
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}
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```