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if statement

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if statement
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有条件地执行代码
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只有在一定条件下是存在的，需要执行其中的代码使用.
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Used where code needs to be executed only if some condition is present.
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目录

[编辑] 语法

if ( expression ) statement_true
if ( expression ) statement_true else statement_false

[编辑] 解释

expression是一个表达式，转换为bool.
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expression shall be an expression, convertible to bool.
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如果计算结果为true，控制被传递到statement_true，statement_false（如果有的话）不执行.
Original:
If it evaluates to true, control is passed to statement_true, statement_false (if present) is not executed.
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否则，控制传递到statement_falsestatement_true还没有执行.
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Otherwise, control is passed to statement_false, statement_true is not executed.
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[编辑] 关键字

if, else

[编辑] 为例

下面的例子演示了几种在某些情况下，if声明
Original:
The following example demonstrates several usage cases of the if statement
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#include <iostream>
 
int main()
{
    int i = 2;
    if (i > 2) {
        std::cout << "first is true" << '\n';
    } else {
        std::cout << "first is false" << '\n';
    }
 
    i = 3;
    if (i == 3) std::cout << "i == 3" << '\n';
 
    if (i != 3) std::cout << "i != 3" << '\n';
    else        std::cout << "i != 3 is false" << '\n';
}

Output: 

first is false
i == 3
i != 3 is false
来自“http://zh.cppreference.com/mwiki/index.php?title=cpp/language/if&oldid=28827”