Features in Web Applications: The For Loop

Question 1

For Loop

Answer 1

• The for loop has the following syntax:
  for (statement 1; statement 2; statement 3) {
  code block to be executed
  }
• Statement 1 is executed (one time) before the execution of the code block.
• Statement 2 defines the condition for executing the code block.
• Statement 3 is executed (every time) after the code block has been executed.

Question 2

statement 1

Answer 2

• Normally you will use statement 1 to initialize the variable used in the loop (i = 0).
• This is not always the case, JavaScript doesn’t care. Statement 1 is optional.
• You can initiate many values in statement 1 (separated by comma):
• Example
  for (i = 0, len = cars.length, text = “”; i < len; i++) {
  text += cars[i] + “<br></br>”;
  }

Question 3

statement 2

Answer 3

• Often statement 2 is used to evaluate the condition of the initial variable.
• This is not always the case, JavaScript doesn’t care. Statement 2 is also optional.
• If statement 2 returns true, the loop will start over again, if it returns false, the loop will end.
• If you omit statement 2, you must provide a break inside the loop. Otherwise the loop will never end. This will crash your browser. Read about breaks in a later chapter of this tutorial.

Question 4

statement 3

Answer 4

• Often statement 3 increments the value of the initial variable.
• This is not always the case, JavaScript doesn’t care, and statement 3 is optional.
• Statement 3 can do anything like negative increment (i–), positive increment (i = i + 15), or anything else.
• Statement 3 can also be omitted (like when you increment your values inside the loop):
• Example
  var i = 0;
  var len = cars.length;
  for (; i < len; ) {
  text += cars[i] + “<br></br>”;
  i++;
  }

Question 5

In the string: “Hello There, Kim!” the “K” represents which letter position?

Answer 5

13

Question 6

What do you think the general purpose of loops is?

Answer 6

In essence, it’s to repeat a set of programming instructions to save us typing many repetitive lines of code and making our programs more efficient.