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Mathematical Assignment Operators

In this exercise, let's consider how we can use variables and math operators to calculate new values and assign them to a variable. Check out the example below:

let x = 4; x = x + 1;

In the example above, we created the variable x with the number 4 assigned to it. On the following line, x = x + 1 increases the value of x from 4 to 5.

Notice, on line two in the example above, to increment x by one we had to write the x variable on the left and right side of the assignment operator (=). Using a variable twice in one expression is redundant and confusing.

To address this, JavaScript has a collection of built-in mathematical assignment operators that make it easy to calculate a new value and assign it to the same variable without writing the variable twice. See examples of these operators below.

let x = 4; x += 2; // x equals 6 let y = 4; y -= 2; // y equals 2 let z = 4; z *= 2; // z equals 8 let r = 4; r++; // r equals 5 let t = 4; t--; // t equals 3

In the example above, operators are used to calculate a new value and assign it to the same variable. Let's consider the first three and last two operators separately:

  1. The first three operators (+=, -=, and *=) perform the mathematical operation of the first operator (+, -, or *) using the number on the right, then assign the new value to the variable.
  2. The last two operators are the increment (++) and decrement (--) operators. These operators are responsible for increasing and decreasing a number variable by one, respectively.
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