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Because the while loop checks the condition/expression before the block is executed, the control structure is often also known as a pre-test loop. Compare this with the do while loop, which tests the condition/expression after the loop has executed. For example, in the languages C, Java, C#, [2] Objective-C, and C++, (which use the same syntax ...
Early BASICs (such as GW-BASIC) used the syntax WHILE/WEND. Modern BASICs such as PowerBASIC provide both WHILE/WEND and DO/LOOP structures, with syntax such as DO WHILE/LOOP, DO UNTIL/LOOP, DO/LOOP WHILE, DO/LOOP UNTIL, and DO/LOOP (without outer testing, but with a conditional EXIT LOOP somewhere inside the loop). Typical BASIC source code:
Visual Basic: Do While condition instructions Loop or Do Until notcondition instructions Loop or While condition instructions Wend (Visual Basic .NET uses End While instead) Do instructions Loop While condition or Do instructions Loop Until notcondition: i must be declared beforehand. For i = first To last «Step 1» instructions Next i
The break statement is used to end a for loop, while loop, do loop, or switch statement. Control passes to the statement following the terminated statement. A function returns to its caller by the return statement. When return is followed by an expression, the value is returned to the caller as the value of the function.
The continue statement discontinues the current iteration of the current control statement and begins the next iteration. The following while loop in the code below reads characters by calling getChar(), skipping the statements in the body of the loop if the characters are spaces:
If xxx1 is omitted, we get a loop with the test at the top (a traditional while loop). If xxx2 is omitted, we get a loop with the test at the bottom, equivalent to a do while loop in many languages. If while is omitted, we get an infinite loop. The construction here can be thought of as a do loop with the while check in the middle. Hence this ...
The syntax varies only slightly from the curly-brace syntax. In each case the opening brace ({) is replaced with a colon (:) and the close brace is replaced with endif;, endwhile;, endfor;, endforeach;, or endswitch;, respectively. [22] Mixing syntax styles within the same control block is not supported.
The basic idea of loop unrolling is that the number of instructions executed in a loop can be reduced by reducing the number of loop tests, sometimes reducing the amount of time spent in the loop. For example, in the case of a loop with only a single instruction in the block code, the loop test will typically be performed for every iteration of ...