Question

for ( ;; ) {
    print "Command>  ";
    $result = <STDIN>;
    print "\n";
    $answer = 0;
    if ( $result == "add" ) {
        for ( $counter = 1; $counter >= 1; $counter++ ) {
            print "Enter the $counter th number:  ";
            $NumberToAdd = <STDIN>;
            if ( $NumberToAdd != "NONE" ) {
                $answer = $answer + $NumberToAdd;
            } else {
                print "\n";
                last;
            }
        }
    } elsif ( $result == "subtract" ) {
        for ( $counter = 1; $counter >= 1; $counter++ ) {
            print "Enter the $counter th number:  ";
            $NumberToSub = <STDIN>;
            if ( $NumberToSub != "NONE" ) {
                $answer = $answer - $NumberToSub;
            } else {
                print "\n";
                last;
            }
        }
    } elsif ( $result == "quit" ) {
        last;
    } else {
        print "Error. Please enter add, subtract, or quit, and press Enter. \n";
    }
    print "The answer to your operation was: $answer \n";
}

现在，如果你在终点线输入quit，它仍然会进入第一个if语句。或者，如果您输入asdfsa，它仍将进入第一个if语句。等

编辑：新的，正确的工作代码如下所示：

for ( ;; ) {
    print "Command>  ";
    chomp( $result = <STDIN> );
    $answer = 0;
    if ( $result eq 'add' ) {
        for ( $counter = 1; $counter >= 1; $counter++ ) {
            print "Enter number $counter to add:  ";
            chomp( $NumberToAdd = <STDIN> );
            if ( $NumberToAdd ne 'NONE' ) {
                $answer = $answer + $NumberToAdd;
            } else {
                last;
            }
        }
    } elsif ( $result eq 'subtract' ) {
        for ( $counter = 1; $counter >= 1; $counter++ ) {
            if ( $counter == 1 ) {
                print "Enter the first number to begin subtracting from:  ";
                chomp( $NumberToSubtractFrom = <STDIN> );
                if ( $NumberToSubtractFrom eq 'NONE' ) {
                    last;
                }
            } elsif ( $counter != 1 ) {
                $countertodisplay = $counter - 1;
                print "Enter number $countertodisplay to subtract:  ";
                chomp( $NumberToSub = <STDIN> );
                if ( $NumberToSub eq 'NONE' ) {
                    last;
                } else {
                    $NumberToSubtractFrom = $NumberToSubtractFrom - $NumberToSub;
                }
            }
        }
        $answer = $NumberToSubtractFrom;
    } elsif ( $result eq 'quit' ) {
        last;
    } else {
        print "Error. Please enter add, subtract, or quit, and press Enter. \n";
    }
    print "The answer to your operation was: $answer \n";
}

Answer 1

错误的运算符用作..

.. Perl有一些运算符的两个版本，一个用于数字，一个用于字符串比较。例如$ a == $ b比较两个数字是否相等，$ a eq $ b比较两个字符串。

详见Equality Operators;注意数字和 stringwise 这两个词。这些值是数字 -equal，即使它们是不同的字符串并且 stringwise - 不同。

以下是快速摘录：

如果左参数在数字上等于到右参数，则二进制“==”返回true。

如果左参数 stringwise equal 到右参数，则二进制“eq”返回true。

第一步是将==的所有错误用法替换为eq。

此外，代码应从$ result中删除尾随换行符，因为"foo" eq "foo\n"为false。有关如何轻松完成此操作，请参阅chomp。

为什么这个检查if子句的perl代码总是默认为第一个if？

1 个答案: