Operators, If and If/Else
Now is a good time to discuss operators in JavaScript. I am also doing to discuss If and If/Else statements becuase this is when you are going to use many of these operators. There are several types of operators, and they are listed and described below:
Arithmetic Operators: These are they symbols used to calculate values.
- "+" Addition
- "-" Subtraction
- "*" Multiplication
- "/" Division
- "%" Modulus (Takes one number and divides it by another number and places the remainder in the variable.)
If you are unfamiliar with Modulus, heres an example of how it works:
| 0 = 4 % 3; 1 = 5 % 2; 3 = 21 % 6; 0 = 15 % 3; |
In arithmetic conditions, JavaScript follows the order of operations. I think in grade school they tauht it as something like, "Please Excuse My Dear Aunt Sally."
- Parenthesis ()
- Unary Operations -
- Mult. and Division (L to R) * and /
- Add and subtraction (L to R) + and -
It is useful to be aware of the order of operations when working with more than 2 numbers. Here is an example of what I mean:
| a = 5; b = 10; c = ((a + b) * 8) / 2; document.write(c); |
Relational Operators: These are used when comparing one or more items and will return a boolean expression.
- "==" Equals
- "<" Less Than
- ">" Greater than
- ">=" Greater than or Equal
- "<=" Less Than or equal
- "!=" Not equal
Logical Operators: used to compare two or more simple conditions at the same time.
- "& &" = and
- "||" = or
Something to go along with the logical operators are what are called, "Truth Tables." Truth tables show all possibilties for logical operators when looking at conditions.
& &: |
||: |
||||
X |
Y |
X& &Y |
X |
Y |
X||Y |
F |
F |
F |
F |
F |
F |
F |
T |
F |
F |
T |
T |
T |
F |
F |
T |
F |
T |
T |
T |
T |
T |
T |
T |
Compound Conditions: This is just where you combine two or more simple conditions with a logical operator. example:
| a=3; b=4; c=5; d=2; if ((a ==3) & & (b ==4)) //<--the compound condition e = c + d; else e = c - d; document.write("e="+e); |
Increment Operator:
To say, x = x + 1:
++x;
x++;
Say you took: y = x++; Whats going to happen?
y will = x
and then x will = x + 1.
Say you took y = ++x; Whats going to happen?
x will = x + 1
then, y = x.
Decrement Operator:
To say, x = x - 1:
--x;
x--;
If you took y = x--; What will happen?
y will = x
and then x will = x - 1.
If you had y = --x; What happens?
x will = x - 1;
then y will = x.
Not as confusing as you migh think. This will help you when using increment and decrement operators to know the value of your variable through the process of the program.
