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JavaScript Basics

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Change the Value in a Variable

3:41 with Guil Hernandez

Once you declare a variable and assign it a value, your program can manipulate what's stored in the variable as it runs, like a score in a game, for example.

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    You've learned how to declare name and assign information or 0:00
    values to variables, as well as how to assign a new value to a variable. 0:03
    Remember, variables hold values that can change. 0:08
    Once you declare a variable and assign it a value, your program can manipulate 0:11
    what's stored in the variable as it runs, like the score in a game for example. 0:15
    You can use variables to do a variety of different things 0:20
    with the value stored in or assigned to them. 0:23
    Remember the variable score, it holds a number value, let's say zero. 0:26
    Earlier you learn that you can change what's inside a variable 0:31
    through reassignment like this, score = 10. 0:36
    Logging score to the console shows that the value of score is now 10. 0:40
    Well, we can change the value of a variable like score, we are overriding 0:46
    the value every time, rather than keeping a running total of the score. 0:52
    Think about if you were programming a game and 0:57
    wanted to keep track of a player score using the variable score. 0:59
    Well instead of overriding the value of score each time a player scores points, 1:02
    you'd most likely want to keep adding to the total score. 1:07
    In other words, instead of completely replacing what's inside the labelled 1:10
    box with something else, we want to add to the current contents of the box. 1:14
    One way to add to the score is like this, score = score + 10. 1:19
    This might look a bit strange. 1:26
    The variable score appears twice in the statement, so how does this work? 1:28
    Remember, when putting a value into a variable, 1:33
    whatever's to the right of the equal sign goes into the variable on the left. 1:37
    In this case, 1:43
    what's on the right is the current contents of the variable score + 10. 1:44
    The sum of the two values is placed back into the variable score. 1:49
    Since score currently equals 0, it's just like saying score = 0 + 10. 1:54
    The idea of accessing a variable to update a variable still might seem a bit strange, 2:02
    but it's really common in programming to update a variable based on the value it 2:06
    already has in it. 2:10
    In fact, it's so 2:12
    common that there's a shorthand method for adding to the contents of a variable. 2:13
    Replace this part here with a + sign and an = sign. 2:17
    This is called an addition assignment operator, and 2:23
    you'll see it a lot in JavaScript. 2:27
    To increase the score by a certain amount, 2:29
    you can use the addition assignment operator to add to its current value. 2:32
    For instance, score += 5. 2:37
    Since the value of score was 10, I added 10 + 5, and now score is 15. 2:42
    You can also add variables representing number values together. 2:52
    For example, declare a new variable named 2:55
    bonusPts and assign it the value 100. 3:01
    I can add the current score value with the value of bonusPts like this, 3:06
    var finalScore = score + bonusPts. 3:14
    We are adding the current value of the variable score plus the value 3:18
    of the variable bonusPts and saving the sum of those values to a third variable, 3:22
    finalScore. 3:27
    Log finalScore to the console, and the result is 115. 3:31

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