However, Perl evaluates the statements from right to left. Let's say we want to find the index of an item from some array and we want that index to use for something else. Since the variable is global, another loop using it would interact with the first one, probably in undesirable ways. If you only wanted to use height inside the loop, it's fine. And you cannot declare a variable in a general expression. 3. Used for iterating(yes, I know about iterators and enhanced loop, but let's use the old for) 2 Variables outside. Can anyone tell me why I cant use a variable inside a while loop? The result is that just because you are in the condition of an if, for, while, or switchdoes not mean that you can declare a variable inside an expression. While Loop in Bash. All Declare does is declare a variable. I guess this is more of a question about scope. The C++ syntax has a special case for 'condition', which has two alternative forms: 1. expression 2. type-specifier-seq declarator = assignment-expression meaning that you can declare a variable *directly* inside the while/if/for/switch, but not elsewhere. Unless they are static, they get created when the function is entered, and get discarded when the function exits. Python doesn't declare variables. Answer (1 of 6): Now-a-days compilers (at least C ones as I do not know about others) are intelligent enough to understand if you are not using the variable outside the loop in spite of declaring it outside, they shall optimise that and try not to put it in registers for nearby operations. Object scope But thereafter, the only way the variables value will become NULL again is through an explicit assignment. For example, i could do something like this with a for loop: you can declare a variable inside any loop(includes do while loop.lol).But remember the scope of that variable is restricted inside the loop. An automatic variable is local to its block (delimited by {}), so it cannot be used as a loop counter if declared within the loop body. BEGIN. Using OOP. The standard allows the condition to declare a variable, however, they have done so by adding a new grammar rule called 'condition' that can be an expression or a declarator with an initializer. It's a matter of variable scope. Code Declaring variables inside or outside of a loop, It's the result of JVM specifications But in the name of best coding practice it is recommended to declare the variable in the smallest possible scope (in this example it is inside the loop, as this is the only place where the variable is used). Create a new on-line program in a new window, with a suitable title and opening comment. Answer (1 of 6): Now-a-days compilers (at least C ones as I do not know about others) are intelligent enough to understand if you are not using the variable outside the loop in spite of declaring it outside, they shall optimise that and try not to put it in registers for nearby operations. The following script does not work: #!/bin/bash # Comparing test1.txt with test2.txt, test1.ini. The problem here is that '(int The output is the same as the first one. It's not a problem to define a variable within a loop. It also means that you can't declare the same variable name inside IF and ELSE blocks. This means the variable life scope is "until it's no longer referenced by any entity". What's bad is to assign a variable within a loop if you could just as well assign it once before the loop runs. Used for iterating(yes, I know about iterators and enhanced loop, but let's use the old for) 2 Variables outside. The output is the same as the first one. We noticed a very strange issue, that when we declare a table variable in a loop, its data persist across iterations. But, f. We shall get to the use of that amazing property to declare variables dynamically. Depending on how complex the right-hand side of the assignment is, this could become rather expensive and might even dominate the . Inside the loop there's an if statement. Depending on how complex the right-hand side of the assignment is, this could become rather expensive and might even dominate the . Then we make a loop with while. Consider this example: SET XACT_ABORT ON. Variables declared inside a function have local scope. Code It's not a problem to define a variable within a loop. 2. type-specifier-seq declarator = assignment-expression meaning that you can declare a variable *directly* inside the while/if/for/switch, but not elsewhere. Answer (1 of 5): 1. Here ,Solution is assign value of variable which is declared inside while loop to another local variable. And then use local variable in main method. Your 2. suggestion is the typical way to use a counter in a while loop, although isolating the counter with an outer block is usually not necessary. I am expecting that when the variable is declared inside the loop it should get reset everytime the loop runs. The value of any variable that has never been assigned to is NULL. int num = 0; while(num <= 10) { System.out.println(num) num = num + 1 } But I don't know how to declare variables and use them in a while loop in a Shell Script. The variable i in while(i--) is different from the variable i defined inside the loop. See Mozilla docs for details.. A pure assignment (without instantiation) is coerced to a boolean via its default return value (the value of the right-hand-side). What I was really aiming at was to declare and use a temporary string variable within the If block to keep the scope local. It also means that you can't declare the same variable name inside IF and ELSE blocks. And you can't declare a loop control variable with "let" inside the loop block as it will not be accessible from the loop context. Most of the time we'll use for loops or while loops. You can't use the variables for the loop scope because you will need the index so your index must be outside the loop . But, the height var would cease to exist when the code exits the loop, so you couldn't use it later. C++ uses machine memory model, . It means that Perl evaluates the condition in the while statement at the beginning of each iteration.. You use the while loop statement modifier only if you have one statement to execute repeatedly based on a condition like the above . WHILE @@FETCH_STATUS = 0. Python references all variables. One of the greatest features of Python is its support for OOP (Object-Oriented Programming). In fact, it's good practice, since identifiers should be confined to the smallest possible scope. Declaring variables using globals is the same as declaration using a dictionary. It has no relation to assignment. At the end of the day, I find no plausible scenario where you would need to do something like this. Can anyone tell me why I cant use a variable inside a while loop? while ( condition is true ) do something % Note: the "something" should eventually result % in the condition being false end Infinite loops: If the action inside the loop does not modify the variables being tested in the loops condition, the loop will "run" forever. However, adding a "this." inside the variable declaration doesn't fix this problem. That is you can't use that variable outside the loop. We also declare the i loop variable and give it a default value of 0. Since the variable is global, another loop using it would interact with the first one, probably in undesirable ways. Within the While loop, we must use SQL Arithmetic Operators to increment and decrements the loop value. A2. C++ uses machine memory model, . There are no more "local" scoping rules in T-SQL. Share Improve this answer Follow answered Apr 26 '17 at 16:55 Basil KuriakoseBasil Kuriakose 2766 bronze badges Add a comment | Yes, it is possible, and perfectly permissible to declare height inside the do/while loop, but there's a problem. Declaring objects in the smallest scope improve . 3. FETCH NEXT FROM cur INTO @id. I am new to shell scripting so I am curious about using While Loops in Shell Script form. Bo Persson May 11 '06 # 6 We shall get to the use of that amazing property to declare variables dynamically. OPEN cur. Hi! For example: Can anyone tell me why I cant use a variable inside a while loop? These variables are created on the stack as part of the function's stack frame. So, since str is not used outside the loop, the smallest possible scope for str is within the while loop. In your example I presume str is not used outside of the while loop, otherwise you would not be asking the question, because declaring it inside the while loop would not be an option, since it would not compile.. 2. A2. This loop continues as long as i is less than ( <) the number of elements in our array ( websites.Length ). 2. If the condition is True, then it executes the code within the BEGIN..END statements. And you can't declare a loop control variable with "let" inside the loop block as it will not be accessible from the loop context. All Declare does is declare a variable. The While loop in SQL Server will check the condition at the beginning of the loop. declare @message nvarchar(max) select * into #errors from [ErrorLog] where ErrorDate > (SELECT DATEADD(minute, -100, GETDATE())) While (Select Count(*) From #errors) > 0 Begin @message = @message + (Select Top 1 ErrorProcedure From #errors) End The following script does not work: #!/bin/bash # Comparing test1.txt with test2.txt, test1.ini. Answer (1 of 5): 1. Write a simple while() loop that reads in an integer. Your 2. suggestion is the typical way to use a counter in a while loop, although isolating the counter with an outer block is usually not necessary. Hi! A variable declared inside a loop will be discarded after the loop ends and the memory of this variable is freed because the variable is local to the loop and not the class. Loops help you to repeatedly execute your command based on a condition. In Java, an array object can hold any form of primitive or non-primitive data. This time I'll show you the while loop and in my Python tutorials I'll get back to the for . In other words, a variable in Python is declared implicitly, by its 1st use in the code. 2. One of the greatest features of Python is its support for OOP (Object-Oriented Programming). Thus they are an essential part not just of data analysis, but general computer science and programming. declare @message nvarchar(max) select * into #errors from [ErrorLog] where ErrorDate > (SELECT DATEADD(minute, -100, GETDATE())) While (Select Count(*) From #errors) > 0 Begin @message = @message + (Select Top 1 ErrorProcedure From #errors) End Yes and no. Using OOP. I have a question regarding how a variable can be called with another variable name inside a loop. declare @message nvarchar(max) select * into #errors from [ErrorLog] where ErrorDate > (SELECT DATEADD(minute, -100, GETDATE())) While (Select Count(*) From #errors) > 0 Begin @message = @message + (Select Top 1 ErrorProcedure From #errors) End Python references all variables. An automatic variable is local to its block (delimited by {}), so it cannot be used as a loop counter if declared within the loop body. Basically int i = 100 shadows the previous int i = 3 and inside the block of the while you're referring to a new variable. I know how to declare a variable and use a while loop in java. The question is a little dated, but I think the answers all miss an important distinction. The problem here is that ' (int c = getchar ())' does not match syntax #2, so must be #1 - an expression. The result is that just because you are in the condition of an if, for, while, or switch does not mean that you can declare a variable inside an . 2. Declaring variables using globals is the same as declaration using a dictionary. But it retains the value from the . while (int c = getchar()) {putchar (c);} Yes. But, f. Python doesn't declare variables. NB: if you have problems with this see the min-exercise in the section "Debugging loops". The scope of local variables should always be the smallest possible. Hi! - Becker's Law My blog My TechNet articles Marked as answer by ibraheem alkilanny2 Tuesday, July 12, 2016 7:30 AM Let's say we want to find the index of an item from some array and we want that index to use for something else. Yes. For every expert, there is an equal and opposite expert. After the value increase, again SQL Server checks the condition. From Declare: The scope of a local variable is the batch in which it is declared. The standard allows the condition to declare a variable, however, they have done so by adding a new grammar rule called 'condition' that can be an expression or a declarator with an initializer. So, the DECLARE variable is actually executed once, in other words, the variable is created once and remains and it doesn't matter if it's created in the loop or outside. I have a question regarding how a variable can be called with another variable name inside a loop. Declare an int variable and initialise it to zero. A variable @test-2 is declared inside the loop. It has no relation to assignment. Code language: Perl (perl) In this example, the while loop statement is placed after another statement. Because if I declare a string s prior to the If statement then it persists after the execution of the If block. DECLARE cur CURSOR LOCAL FOR SELECT id FROM someTable. 1. To demonstrate a while() loop. A variable declared inside a loop will be discarded after the loop ends and the memory of this variable is freed because the variable is local to the loop and not the class. What's bad is to assign a variable within a loop if you could just as well assign it once before the loop runs. So, conclusion, undoubtedly, is that setting variable to array length and then usin You can't use the variables for the loop scope because you will need the index so your index must be outside the loop . However, adding a "this." inside the variable declaration doesn't fix this problem. In fact, it's good practice, since identifiers should be confined to the smallest possible scope. That is, a while loop expects an expression that evaluates to a conditional, i.e., a boolean or value that can be converted to a boolean. Answer (1 of 7): You cannot use variable which is declared inside loop in main method just because it's scope is only within that loop. BEGIN TRAN myTrans. 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