while allow you to loop code based on the result of a comparison made on each loop:
x = 1 while x < 100 puts x # from w w w . j a v a 2s .co m x = x * 2 end
Here, you have a while block that denotes a section of code that is to be repeated over and over while the expression x < 100 is satisfied.
Therefore, x is doubled loop after loop and printed to the screen.
Once x is 100 or over, the loop ends.