The while construct consists of a block of code and a condition / expression. The condition / expression is evaluated, and if the condition / expression is true, the code within the block is executed. This repeats until the condition / expression becomes false. 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.
the while loop is this type of loop
pre-test loop