What is the difference between a repeat until and a while do loop?

Answer 1

Repeat until loops run until a condition is true. They repeat at the end of the loop and they will always run at least once.

While do loops will only run while a condition is true. They may not run at all.

Answer 2

There is no "until" loop in C, C++, or Java. Are you thinking do {} while ()?

If so, the while loop tests the condition at the top...

while (condition) statement;

... while the do while loop tests the condition at the bottom ...

do statement; while (condition);

... In the first example, if the condition if false to start with, the loop will never execute, but in the second example, the loop will always execute at least once.

Answer 3

for while

1. the while condition is checked
2. if true, execute the while block
3. if false, exit the while loop
4. go back to 1

for until

1. execute the until block of code
2. check the until condition
3. if true, end
4. else go back to 1

The biggest difference is that while checks the condition and if it's initially false never executes the block of code, while an until loop always executes it's block of code at least once.