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if statement

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Conditional execution statements
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if statement
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Used where code needs to be executed only if some condition is present.
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目次

[編集] 構文

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

[編集] 説明

expressionは、boolに変換式でなければならない.
Original:
expression shall be an expression, convertible to bool.
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それはtrueに評価された場合、制御がstatement_trueに渡され、statement_false(存在する場合)が実行されません.
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If it evaluates to true, control is passed to statement_true, statement_false (if present) is not executed.
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そうしないと、コントロールがstatement_falseに渡され、statement_trueは実行されません.
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Otherwise, control is passed to statement_false, statement_true is not executed.
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[編集] キーワード

if, else

[編集]

次の例では、if文のいくつかの使用例を示しています
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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