For example, if your variable has a value you didn't expect, it can be much easier to figure out where the value came from if the variable has a limited scope. If a variable is global, its value could be changed anywhere in the code, meaning that you need to understand the whole program to know what will happen to the variable. Why, you might be wondering, wouldn't you make all your variables global? After all, if I don't know where I might need a variable, why should I limit its scope to just one function? The answer is that it can make it easier to figure out what happens to it. That is, even though you've declared pin somewhere in your program, you're trying to use it somewhere outside its scope. You'll get the same message as before: 'error: 'pin' was not declared in this scope'. When you assign one variable to another, you're making a copy of its value and storing that copy in the location in memory associated with the other variable. If you include the preceding statement in a program without the first statement above, you'll get a message like: 'error: pin was not declared in this scope'. Note that you have to declare a variable before you can assign a value to it. That is, the name of the variable is permanently associated with a type only its value changes. Notice that we don't specify the type of the variable: it's not changed by the assignment. Will change the value of the variable to 12. Most importantly, you can change the value of a variable using an assignment (indicated by an equals sign). a program controlling an RGB LED might have variables called redPin, greenPin, and bluePin).Ī variable has other advantages over a value like a number. Also, you can use a descriptive name to make the significance of the variable clear (e.g. So if you later decide to change from pin 13 to pin 12, you only need to change one spot in the code. The advantage of a variable in this case is that you only need to specify the actual number of the pin once, but you can use it lots of times. In this case, you don't actually need to use a variable, this statement would work just as well: It is the value of pin (13) that will be passed to the pinMode() function.

Later on in the program, you can refer to this variable by its name, at which point its value will be looked up and used. For example, this statement (called a declaration):Ĭreates a variable whose name is pin, whose value is 13, and whose type is int. A variable is a place to store a piece of data.

Fminer change variable data