C Legal Variable Names

Variables are reference location names. The values we use in a program are stored in locations. Variables provide a way or abstraction to access these locations. A variable, in simple terms, is a storage space to which part of the memory is allocated. Basically, a variable is used to store some form of data. Different types of variables require different amounts of memory, different types of locations, and a specific set of operations that can be applied to them. In the example above, x and y are automatic variables. The only difference is that the variable there is explicitly declared with the auto keyword. Variable declaration: A typical variable declaration takes the following form: you will see more instances of the directive #define later in the text. It`s a good convention to write #defined words in capital letters, so that a programmer knows that this is not a variable you declared, but a macro #defined. There is no need to complete a preprocessor directive such as #define with a semicolon; In fact, some compilers may warn you of unnecessary tokens in your code when you do this. 5.

External variables: External variables can be shared by multiple C files. We can declare an external variable with the external keyword. When you declare a local variable as static, it is created like any other variable. However, if the variable leaves the scope (that is, the block in which it was local is terminated), the variable remains in memory and retains its value. The variable remains in memory until the end of the program. Although this behavior is similar to that of global variables, static variables still obey range rules and therefore cannot be called outside their range. This is called static storage time. All variables in C are typed. That is, each declared variable must be assigned as a specific variable type. Is it possible to have a separate explanation and definition? Is this possible with external variables and functions? See question 1 for more details.

This function changes the value of the environment variable. The following sample program demonstrates how to modify an existing environment variable value. It is not allowed to use the same name for multiple variables in the same range. Therefore, if you are working with other developers, you should take steps to avoid using the same name for global variables or function names. Some large projects follow naming guidelines[1] to avoid duplicate names and ensure consistency. 1) An identifier/variable name should only begin with an alphabet or underscore (_), no other special characters, numbers are allowed as the first character of the identifier/variable name. Variables in C have the same meaning as variables in algebra. A variable in C is a storage unit that defines a memory space to store a value and can take different values at different times during program execution. external: External simply tells us that the variable is defined elsewhere and not in the same block in which it is used. Basically, the value is assigned to it in another block and this can also be overwritten/changed in another block.

Thus, an external variable is nothing more than a global variable that is initialized with a legal value where it is declared for use elsewhere. It can be called in any function/block. A normal global variable can also be rendered external by placing the keyword `external` before its declaration/definition in any function/block. This basically means that we don`t initialize a new variable, but we just use/access the global variable. The main purpose of using external variables is to be able to access them between two different files that are part of a large program. In the code above, both functions can use the global variable x because we already have global variables that all functions can access. As the last example shows, some words are reserved as keywords in the language, and these cannot be used as variable names. In this C tutorial, we learned how to declare, define, and initialize a variable in the C programming language.

We will learn the scope of the variables in the next tutorial. This statement instructs the compiler to create a variable named some_number and map it to a location on the computer. We also tell the compiler the type of data stored at this address, in this case an integer. Note that in C we need to specify the type of data that a variable stores. This allows the compiler to know how much total memory to reserve for the data (on most modern computers, an int is 4 bytes long). In the next section, we will look at other types of data. In the C programming language, all variables used in the program must be declared before being used. The variable must be declared in the declarations section of the feature set (this can be a primary function or another user-defined function). The declaration section begins at the beginning of any function immediately after the brace is opened.

To specify the storage location, each variable must be given a unique name (identifier). Variable names are only the symbolic representation of a place. For example, because C is a relatively weak programming language, before a C program can use memory to store a variable, it must consume the memory needed to store the values of a variable. This is done by declaring variables. Variable declaration is how a C program displays the number of variables needed, their names, and the amount of memory they need. The C programming language applies the following rules for naming a variable. In the following example, we declared global variables and local variables and initialized these variables. Note: You should always try to give descriptive names to variables. For example, firstName is a better variable name than fn. First, it`s easier to think of variables as placeholders for values, similar to mathematics.

You can think of a variable as equivalent to the value assigned to it. So if you have a variable i that is initialized to 4 (also set), it follows that i + 1 is equal to 5. However, an experienced C programmer is aware of the invisible layer of abstraction that runs right under the hood: that a variable is a substitute for the memory address where the data can be found, not the data itself. You will gain more clarity on this point by inquiring about pointers. If you want to set a variable whose value cannot be changed, you can use the const keyword. This creates a constant. For example, we can define multiple variables of the same data type in a single row using the comma operator (,) as the separator. 9) Keep the indent when declaring/defining an identifier/variable, in the last point, the declared variables are not in a correct indent, you must write as follows: Several variables can be declared with a statement, as follows: If you declare a function or a global variable as static, you cannot use the external keyword (see below) from other files in your project to access the function or to the variable enter. This is called a static link.