95 lines
2.0 KiB
Markdown
95 lines
2.0 KiB
Markdown
---
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title: C++ If Statement
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localeTitle: C ++ If Statement
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---
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# IF声明。
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**if语句有什么作用？**
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* `if`语句计算括号内存在的测试表达式。
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* `if`语句使用关系运算符和逻辑运算符来生成逻辑表达式。
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* * *
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`if`语句的一般形式：
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```cpp
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if (Test Expression / Condition)
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{
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// Block of statements if test expression is True
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}
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```
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如果测试表达式的值为**true** ，则为块 执行if语句中的代码。
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如果测试表达式的值为**false** ，则为块 跳过if语句中的代码并继续执行代码。
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示例`if`语句：
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```cpp
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int a = 10;
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// true statement
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if (a < 20)
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{
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// execute this block of code
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}
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// false statement
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if (a < 0)
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{
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// Skip this block of code.
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}
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```
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示例在C ++中：
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```cpp
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// Program to check if number entered by the user is positive
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// If negative, the block of code is skipped
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#include <iostream>
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using namespace std;
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int main()
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{
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int no ;
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cout << "Enter a number: ";
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cin >> no;
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// if statement to check if the number is positive
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if ( no > 0)
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{
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cout << "You have entered a positive number: " << no << endl;
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}
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// If number is not positive, then if statement is skipped a program continues
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cout << "This step is always printed" << endl;
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return 0;
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}
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```
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**输出：**
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输出1：
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```
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Enter a number: 5
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You have entered a positive number: 5
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This step is always printed
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```
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This is the output when the number entered is positive.
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OUTPUT 2:
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```
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输入一个数字：-1 始终打印此步骤 \`\`\` 这是输入数字为负数时的输出。
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[亲自尝试一下代码吧！ :)](https://repl.it/Mg9X)
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_祝贺。祝贺。这是关于IF声明的文章的结尾_
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**祝大家好运**
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**快乐的编码！ :)**
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**随意在FreeCodeCamp的GitHub页面或[FreeCodeCamp的论坛](https://forum.freecodecamp.org/)上询问任何问题[。](https://forum.freecodecamp.org/)** |