learning-journal

Kyle's Learning Journal

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Operators and Loops Notes

Comparison Operators Evaluating Conditions

• Is Equal to (==)
  • compares two values to see if they’re the same
• Is Not Equal to (!=)
  • Compares two values to see if they are not the same.
• Strict Equal to (===)
  • Compares two values to check that both the data type and value are the same.
• Strict Not Equal to (!==)
  • Compares two values to check that both the data type and value are not the same.
• Greater Than (<)
  • Checks number on the left is greater than the number on the right.
• Less Than (<)
  • Checks if number on the left is less than number on the right.
• Greater Than or Equal to (>=)
  • Checks number on the left is greater than or equal to the number on the right.
• Less Than or Equal to (<=)
  • Checks number on left is less than or eual to the number on the right

    Comparison Operator Anatomy

    (score >= pass)

• “score” = operand
• “pass” = operand
• ”>=” = comparison operator
• ”()” = enclosing brackets

Logical Operators

• && = logical and
  • tests more than one condition
  • ((2<5) && (3>=2)) returns true

• = logical or

  • tests at least one condition

  • ((2<5)

    (2>1)) returns true

• ! = logical not
  • operator takes a single Boolean value and inverts it.
  • !(2<1) returns true
    

((5 < 2) && (2 >= 3))

• (5<2) = expression 1
• (2 >= 3) = expression 2
• && = logical operator
• ((5 < 2) && (2 >= 3)) = expression 3

Loops

Loops check a condition. If it returns true, a code block will run. The condition will be checked again and if still true, the code block will run again. It repeats until the condition returns false.

Common Types of Loops

• For
  • Runs code specific amount of times. The condition is usually a counter which is used to tell how many times the loop should run.
• While
  • Don’t know how many times loop should run. Condition doesnt have to be a counter, and code will continue to loop for as long as the condition is true.
• Do While
  • Similar to while loop but it will always run the statements in curly braces at least once, even if condition is false.

for (var i = 0; i < 10; i++) {
    document.write(i);
}

• “for” = keyword
• ”{}” = curly bracket
• “document.write(i);” = code to execute during loop
• “for (var i = 0; i < 10; i++) = condition(counter)

Loop Counters

A “for” loop uses a counter as a condition. This tells the code to run a specified amount of times. Below you’ll see the condition is made up of three statements:

• Initialization
  • var i = 0;
  • Create a variable and set it to 0. This variable is called i, and acts as the counter.
• Condition
  • i < 10
  • The will run until it hits a specified number.
• Update
  • i++
  • Every time the loop runs the content in the curly brackets it adds one to the counter.

While Loops

- var i = 1;     //Set counter to 1
- var msg = '';  //Message
// Store 5x table in a variable
while (i < 10) {
    msg += i + ' x 5 = ' + (i * 5) + '
';
    i++;
}
document.getElementById('answer').innerHTML = msg;