using the #define preprocessor directive with the syntax #define, and.
#HOW TO USE PRINTF IN C FOR ASC HOW TO#
In this tutorial, you've learned how to define constants: Thus the const qualifier renders a true constant that's immune to changes, and cannot be altered during the execution of the program. You'll see that the program doesn't compile successfully.Īnd the error message reads: error: assignment of read-only variable 'student_id' meaning that you can only read the value of STUDENT_ID and not assign a value to it. STUDENT_ID = 207 // modifying a true constant: NOT POSSIBLE
Let's now try modifying the const variable STUDENT_ID.
This means that if int my_var = 2 is the definition, you can assign a different value to my_var using a simple assignment statement like my_var = 3. However, you can always reassign values of a variable. In C, you cannot redefine an existing variable.įor example, if int my_var = 2 is the first definition, your program won't compile successfully if you try redefining my_var as int my_var = 3.
#HOW TO USE PRINTF IN C FOR ASC CODE#
You can see that the code works as expected. Printf("Student ID: %d is taking the class %d\n", STUDENT_ID, COURSE_CODE)
This is shown in the code snippet below: #include Include the qualifier const in the respective definitions.Since they're both integers, you can define them to be of the int data type, taking the intended values: 27 and 502.Now you'll define them as constants using the const qualifier. How to Declare Constants Using const Qualifier Exampleįrom the previous example, you have the constants STUDENT_ID and COURSE_CODE. ▶ Head on to the next section to modify the previous example using const. And trying to modify it elsewhere in the program will throw errors during compilation. The const qualifier makes the variable read-only. To make a constant, you only need to add the const qualifier to this statement as follows: const = Adding the const keyword in the definition of the variable ensures that its value remains unchanged in the program. In C, = is the syntax to declare a variable of type, and to assign it the value. How to Use the const Qualifier to Define Constants in C Head on to the next section to learn about the const qualifier. So you now know that the #define constants are in some sense not true constants as you can always redefine them. Notice how the redefined value of 207 has been used as the STUDENT_ID, overwriting the previously defined value 27. #define STUDENT_ID 207 //redefinition of a #define constant.ĭepending on your compiler, you may get a warning that you're trying to redefine an already-defined constant.Īnd the value in the most recent definition will be used. And it will compile and execute without errors. As the printf() function can print out formatted strings, the two occurrences of the format specifiers %d (for decimal integers) are replaced by 27 and 502.Īlthough #define lets you define constants, you should be careful not to redefine them elsewhere in the program.įor example, the code below, you've redefined STUDENT_ID.Printf("Student ID: %d is taking the class %d\n", 27, 502) So the body of the main() function will now be: The preprocessor replaces STUDENT_ID and COURSE_CODE by 27, and 502, respectively.Printf("Student ID: %d is taking the class %d\n", STUDENT_ID,COURSE_CODE) How to Declare Constants Using #define ExampleĬonsider the following code snippet, where you have two constants STUDENT_ID and COURSE_CODE. ▶ In the next section, you'll see an example using #define to declare C constants. It's a good practice to include the definition of all constants after the header files in your program, as shown below: #include In C, the preprocessors process the source code ahead of compilation to produce the expanded source code. Before the compilation of the program, the preprocessor replaces all occurrences of with.is a placeholder for the value that takes.It's recommended that you name constants in the uppercase, as it helps differentiate them from other variables defined in the program.is a placeholder for the name of the constant.One of the common ways to define constants in C is to use the #define preprocessor directive, as shown below: #define How to Use #define to Define Constants in C In this tutorial, you'll learn how to use #define and the const qualifier to define them. You can define constants in C in a few different ways. In the C language, you'll likely define them as constants. When you're programming, there are times when you'll want the values of certain variables to remain unchanged.
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