Syntax for while loop
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.
The basic syntax of a while
loop:
while (condition) {
// code to be executed
}
Explanation:
- The
while
loop starts withi
equal to 1. The loop will continue to execute as long asi
is less than or equal to 5. - In each iteration of the loop, the value of
i
is printed to the console usingconsole.log(i)
, and theni
is incremented by 1 using thei++
shorthand fori = i + 1
.
Here's what each part of the while
loop does:
condition
: This is a condition that is evaluated before each iteration of the loop. If the condition is true, the loop will execute; otherwise, the loop will terminate.code to be executed
: This is the code that will be executed in each iteration of the loop as long as the condition is true.
Here's an example of a while
loop that counts from 1 to 5 and prints each number to the console:
let i = 1;
while (i <= 5) {
console.log(i);
i++;
}
In this example:
- The
while
loop starts withi
equal to 1. The loop will continue to execute as long asi
is less than or equal to 5. - In each iteration of the loop, the value of
i
is printed to the console usingconsole.log(i)
, and then i is incremented by 1 using thei++
shorthand fori = i + 1
.
You can also use a while
loop to iterate over the elements of an array:
const numbers = [1, 2, 3, 4, 5];
let i = 0;
while (i < numbers.length) {
console.log(numbers[i]);
i++;
}
In this example:
- The
while
loop starts withi
equal to 0. The loop will continue to execute as long asi
is less than the length of thenumbers
array. - In each iteration of the loop, the value of
numbers[i]
is printed to the console usingconsole.log(numbers[i])
, and theni
is incremented by 1 using thei++
shorthand fori = i + 1
.
The Do While Loop
The do...while
loop is similar to the while loop, but it guarantees that the loop body will be executed at least once, even if the condition is initially false.
The basic syntax of the do...while
loop is:
do {
// code to be executed
} while (condition);
The loop will continue to execute the code block as long as the condition remains true.
However, the code block will always be executed at least once, regardless of the initial state of the condition.
Here is an example that uses a do...while
loop to display the numbers from 1 to 5 in the console:
let i = 1;
do {
console.log(i);
i++;
} while (i <= 5);
In this example:
- The loop will execute at least once, even though the condition
i <= 5
is initially false. - The loop will continue to execute as long as
i
is less than or equal to 5, and each iteration will increment the value ofi
by 1. The output of this code in the console will be:
1
2
3
4
5