Any loop that can be written as a do-while loop can also be written as a while loop.

Q: Which type of loop repeats a statement or set of statements as long as the Boolean expression is false?

A while loop is a control flow statement that allows code to be executed repeatedly based on a given Boolean condition. The while loop can be thought of as a repeating if statement.

Q: Which of the following causes a statement or set of statements to repeat as long as a condition is true?

A loop is a control structure that causes a statement or group of statements to repeat.

Q: Which two statements are true about the while loop?

Which two statements are true about the while loop. The statement in a while loop will execute zero or more times. If the condition of a pre-test loop is false, the statements in the loop are never executed.

Q: Which loop is specifically designed to do a counter controlled loop that is to initialize test and increment a counter variable?

A loop that repeats a specific number of times is known as a count-controlled loop. Count-controlled loops are so common that C++ provides a type of loop specifically for them. It is known as the for loop. The for loop is specifically designed to initialize, test, and update a counter variable.

Loops

Loops can execute a block of code as long as a specified condition is reached.

Inhaltsverzeichnis Show

Java While Loop
The Do/While Loop
Using do...while
Using an assignment as a condition
Specifications
Browser compatibility
Which type of loop repeats a statement or set of statements as long as the Boolean expression is false?
Which of the following causes a statement or set of statements to repeat as long as a condition is true?
Which two statements are true about the while loop?
Which loop is specifically designed to do a counter controlled loop that is to initialize test and increment a counter variable?

Loops are handy because they save time, reduce errors, and they make code more readable.

Java While Loop

The while loop loops through a block of code as long as a specified condition is true:

Syntax

while (condition) {
  // code block to be executed
}

In the example below, the code in the loop will run, over and over again, as long as a variable (i) is less than 5:

Note: Do not forget to increase the variable used in the condition, otherwise the loop will never end!

The Do/While Loop

The do/while loop is a variant of the while loop. This loop will execute the code block once, before checking if the condition is true, then it will repeat the loop as long as the condition is true.

Syntax

do {
  // code block to be executed
}
while (condition);

The example below uses a do/while loop. The loop will always be executed at least once, even if the condition is false, because the code block is executed before the condition is tested:

Example

int i = 0;
do {
  System.out.println(i);
  i++;
}
while (i < 5);

Try it Yourself »

Do not forget to increase the variable used in the condition, otherwise the loop will never end!

The do...while statement creates a loop that executes a specified statement until the test condition evaluates to false. The condition is evaluated after executing the statement, resulting in the specified statement executing at least once.

Try it

Syntax

do
  statement
while (condition)

statement

A statement that is executed at least once and is re-executed each time the condition evaluates to true. To execute multiple statements within the loop, use a block statement ({ /* ... */ }) to group those statements.

condition

An expression evaluated after each pass through the loop. If condition evaluates to true, the statement is re-executed. When condition evaluates to false, control passes to the statement following the do...while.

Note: Use the break statement to stop a loop before condition evaluates to true.

Examples

Using do...while

In the following example, the do...while loop iterates at least once and reiterates until i is no longer less than 5.

let result = "";
let i = 0;
do {
  i += 1;
  result += `${i} `;
} while (i > 0 && i < 5);
// Despite i === 0 this will still loop as it starts off without the test

console.log(result);

Using an assignment as a condition

In some cases, it can make sense to use an assignment as a condition — but when you do, there's a right way to do it, and a wrong way; the while documentation has a Using an assignment as a condition section with an example showing a general best-practice syntax you should know about and follow.

Specifications

Specification
ECMAScript Language Specification # sec-do-while-statement

Browser compatibility

BCD tables only load in the browser

Within the conditional expression of a while...end block, logical operators & and | behave as short-circuit operators. This behavior is the same as && and ||, respectively. Since && and || consistently short-circuit in conditional expressions and statements, it is good practice to use && and || instead of & and | within the expression. For example,

x = 42;
while exist('myfunction.m','file') && (myfunction(x) >= pi)
    disp('Expressions are true')
    break
end

The first part of the expression evaluates to false. Therefore, MATLAB does not need to evaluate the second part of the expression, which would result in an undefined function error.

Which type of loop repeats a statement or set of statements as long as the Boolean expression is false?

A while loop is a control flow statement that allows code to be executed repeatedly based on a given Boolean condition. The while loop can be thought of as a repeating if statement.

Which of the following causes a statement or set of statements to repeat as long as a condition is true?

A loop is a control structure that causes a statement or group of statements to repeat.

Which two statements are true about the while loop?

Which two statements are true about the while loop. The statement in a while loop will execute zero or more times. If the condition of a pre-test loop is false, the statements in the loop are never executed.

Which loop is specifically designed to do a counter controlled loop that is to initialize test and increment a counter variable?

A loop that repeats a specific number of times is known as a count-controlled loop. Count-controlled loops are so common that C++ provides a type of loop specifically for them. It is known as the for loop. The for loop is specifically designed to initialize, test, and update a counter variable.

Any loop that can be written as a do-while loop can also be written as a while loop.

Loops

Java While Loop

Syntax

The Do/While Loop

Syntax

Example

Try it

Syntax

Examples

Using do...while

Using an assignment as a condition

Specifications

Browser compatibility

See also

Which type of loop repeats a statement or set of statements as long as the Boolean expression is false?

Which of the following causes a statement or set of statements to repeat as long as a condition is true?

Which two statements are true about the while loop?

Which loop is specifically designed to do a counter controlled loop that is to initialize test and increment a counter variable?

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