How Do-While Loops Work in Computer Programming

For Loops

Do-while loops have a similar distinction with for loops. A for loop defines a variable, specifies how long the loop should be run, and sets a behavior for the end of each iteration.computer science computer science computer science computer science computer science

Here’s a simple for loop for comparison:

for (int i = 0; i < 5; i++) {
  output "The loop has run " + i + " times.";
}

This highlights a good contrast between do-while and for loops — you know exactly how many times a for loop will run because you set up the conditions at the start. If you modify the above code into a do-while loop like this:

do {
  output "The loop has run " + i + " times.";
  i++;
} while (i < 5);

You could end up with an issue when the loop runs. If you didn’t initialize i somewhere else, you don’t know what its value will be when the do portion runs — and it will run at least once. If i was 500 when this loop ran, the output here would be inaccurate.computer science computer science computer science computer science computer science

In summary:

  • A do-while loop is useful when you want to execute a command at least once, and continually until a condition is false.
  • A while loop lets you repeat a block of code as long as a condition is true, and stop as soon as the condition is no longer true.
  • A for loop lets you specify exactly how many times the loop should run by setting your own parameters.
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