A do...while loop is similar to a while loop, except that a do...while loop is guaranteed to execute at least one time. 

Syntax : 
do {
   // Statements
}while(Boolean_expression);
Notice that the Boolean expression appears at the end of the loop, so the statements in the loop execute once before the Boolean is tested.

If the Boolean expression is true, the control jumps back up to do statement, and the statements in the loop execute again. This process repeats until the Boolean expression is false.