if-statement

问题 This question already has answers here : Calling dynamic variable in PowerShell (2 answers) Closed last year . I am attempting to do something similar to the following ... New-Variable -Name "state_$name" -Value "True" if ("state_$name" -eq "True") { Write-Host "Pass" } else { Write-Host "Fail" } I have attempted this a number of different ways but it is not working exactly how I would like it to work. I need to write the if statement to account for a dynamic variable as these values will

问题 This question already has answers here : Calling dynamic variable in PowerShell (2 answers) Closed last year . I am attempting to do something similar to the following ... New-Variable -Name "state_$name" -Value "True" if ("state_$name" -eq "True") { Write-Host "Pass" } else { Write-Host "Fail" } I have attempted this a number of different ways but it is not working exactly how I would like it to work. I need to write the if statement to account for a dynamic variable as these values will

问题 I've been looking for a MongoDb-like ( http://docs.mongodb.org/manual/applications/read/#find, docs.mongodb.org/manual/reference/operators/ ) query expression object evaluation function implementation or a class. It may cover not all the advanced features, and should have extensible architecture. MongoDB-like query expression objects are easy for understanding and usage , providing ability to write clean, self-explaining code, because both query and objects to search in, are associative

问题 For example, can I do: if ($my_array = wp_get_category($id)) { echo "asdf"; } else { echo "1234"; } If nothing is returned by the function, I want to go into the else statement. 回答1: Yes, that will work, and the pattern is used quite often. If $my_array is assigned a truthy value, then the condition will be met. CodePad. <?php function wp_get_category($id) { return 'I am truthy!'; } if ($my_array = wp_get_category($id)) { echo $my_array; } else { echo "1234"; } The inverse is also true... If

问题 For example, can I do: if ($my_array = wp_get_category($id)) { echo "asdf"; } else { echo "1234"; } If nothing is returned by the function, I want to go into the else statement. 回答1: Yes, that will work, and the pattern is used quite often. If $my_array is assigned a truthy value, then the condition will be met. CodePad. <?php function wp_get_category($id) { return 'I am truthy!'; } if ($my_array = wp_get_category($id)) { echo $my_array; } else { echo "1234"; } The inverse is also true... If

问题 I've been trying to optimize my code to make it a little more concise and readable and was hoping I wasn't causing poorer performance from doing it. I think my changes might have slowed down my application, but it might just be in my head. Is there any performance difference between: Command.Parameters["@EMAIL"].Value = email ?? String.Empty; and Command.Parameters["@EMAIL"].Value = (email == null) ? String.Empty: email; and if (email == null) { Command.Parameters["@EMAIL"].Value = String

问题 I'm using MySQL with PHP and I need to do something like this (pseudocode): if (sql row exists where username='bob') { // do this stuff } 回答1: If you are using mysql database, then use the following - $query = "SELECT username from my_table where username='bob'"; $result = mysql_query($query); if(mysql_num_rows($result) > 0) { // row exists. do whatever you would like to do. } If you would like to use PDO (PHP Data Object), as alex suggested, then use the following code - $dbh = new PDO(

问题 If I write two SELECT statements in a IF EXISTS condition with a AND clause in between these select queries, does both queries get executed even if the first SELECT returns false? IF EXISTS (SELECT....) AND EXISTS(SELECT ....) BEGIN END Does the SQL Server Engine execute both the SQL Statement in this scenario? Thanks Krish 回答1: I would rewrite the test as IF CASE WHEN EXISTS (SELECT ...) THEN CASE WHEN EXISTS (SELECT ...) THEN 1 END END = 1 This guarantees short circuiting as described here

问题 This question already has answers here : Why would you use an assignment in a condition? (11 answers) Closed 2 years ago . I recently just lost some time figuring out a bug in my code which was caused by a typo: if(a=b) instead of: if(a==b) I was wondering if there is any particular case you would want to assign a value to a variable in a if statement, or if not, why doesn't the compiler throw a warning or an error ? 回答1: if (Derived* derived = dynamic_cast<Derived*>(base)) { // do stuff with

问题 Java documentation says The Java compiler generates generally more efficient bytecode from switch statements that use String objects than from chained if-then-else statements. AFAIK even String in switch uses .equals() internally in a case sensitive manner. So what efficiency do they mean in this context. Faster compilation? Less bytecodes ? better performance? 回答1: Using a switch statement is faster than equals (but only noticeably when there are more than just a few strings) because it