do is a C programming keyword used for iteration loops when paired with the while keyword.

int i = 0;
do {
  printf("Hi mom!\n");
} while ( i != 5 );

The above code prints Hi mom! five times. Why bother with this and not just use a straight while loop? Well, whereas a while loop might not be executed at all if the conditional is false, a do loop will always be executed at least once. The conditional isn't even looked at by the program until the loop has executed once.

Getting your whiles and dos mixed up? Just remember that the while comes at the end of a do loop, so the conditional isn't evaluated until the end.