C Constant

In the realm of computer science, understanding the concept of C Constants is crucial to mastering the C programming language. As you delve into this significant topic, you will explore its definition, types, implementation, and practical applications. Starting with the fundamental question of what a C Constant is, this article will provide comprehensive insights into integer, floating-point, and character constants in C. Furthermore, you will learn the nuances of defining, implementing, and using C Constants in your programs, including constant expressions and enumeration constants. To help solidify these concepts, examples and real-life applications are discussed, from constant arrays to constant pointers in C. By gaining a thorough understanding of C Constants, you will not only enhance your programming skills but also elevate the overall efficiency and reliability of your code.

Get started Sign up for free
C Constant C Constant

Create learning materials about C Constant with our free learning app!

  • Instand access to millions of learning materials
  • Flashcards, notes, mock-exams and more
  • Everything you need to ace your exams
Create a free account

Millions of flashcards designed to help you ace your studies

Sign up for free

Convert documents into flashcards for free with AI!

Table of contents

    What is a C Constant?

    A C constant is an immutable value or data that remains unchanged throughout the execution of a program. In C programming, constants are used to provide fixed data or values to a program, ensuring efficiency and consistency. Using constants instead of variables with fixed values can prevent accidental modifications and enhance the code readability.

    A C Constant refers to a value that remains unchanged during the execution of a program. It is used to provide fixed data or values to the program, ensuring efficiency and consistency.

    Types of C constants

    In C programming, constants can be broadly categorized into the following types:

    • Integer constants
    • Floating-point constants
    • Character constants

    Integer constants in C

    Integer constants are whole numbers that can be positive or negative. They are expressed in the base of 10 (decimal), base of 8 (octal), or base of 16 (hexadecimal). A few rules apply to integer constants:

    • No commas or blanks are allowed within the constant.
    • Decimal constants must not be prefixed with zeroes.
    • Octal constants are prefixed with a '0' (zero).
    • Hexadecimal constants are prefixed with '0x' or '0X'.

    Examples of Integer Constants:

    • 10 (Decimal constant)
    • 012 (Octal constant)
    • 0xA (Hexadecimal constant)

    Floating-point constants in C

    Floating-point constants represent real numbers and can be represented in two forms: fractional form and exponent form. The fractional form includes a decimal point, while the exponent form includes an 'e' or 'E', followed by an integer exponent. A few rules apply to floating-point constants:

    • At least one digit must be present before and after the decimal point in the fractional form.
    • An exponent in exponent form must be a whole number.
    • The use of 'f' or 'F' suffix denotes a single-precision floating-point constant, whereas 'l' or 'L' denotes a long double. Without these suffixes, the constant is considered a double.

    Examples of Floating-point Constants:

    • 123.45 (Fractional form)
    • 1.23e2 (Exponent form)
    • 3.14F (Single-precision constant)

    Character constants in C

    Character constants represent single characters, enclosed within single quotes. They can be letters, digits, or special characters, as well as escape sequences. Each character constant is of the integer type, corresponding to the integer value of the character in the ASCII table.

    Examples of Character Constants:

    • 'A' (Character constant)
    • '5' (Digit constant)
    • '\$' (Special character constant)
    • '\n' (Escape sequence constant - newline)

    While string constants in C might seem similar to character constants, they are collections of characters enclosed within double quotes. Unlike character constants, string constants are arrays of characters, terminated by a null character ('\0').

    Implementing C Constants in Programming

    In C programming, constants are defined using the 'const' keyword, followed by the data type, and then the constant name, which is assigned a specific, unchangeable value. The syntax for defining a C constant is:

    const data_type constant_name = value;

    It is a good practice to use uppercase letters for constant names to differentiate them from variable names. Additionally, constants can be defined as preprocessor directives (macros) using the '#define' directive, as follows:

    #define CONSTANT_NAME value

    This method does not involve using the 'const' keyword or declaring a data type for the constant. Instead, the preprocessor replaces all occurrences of the constant name with their corresponding value during the compilation process.

    Examples of defining constants in C:

    const int SIZE = 10;            // using the 'const' keyword
    const float PI = 3.14159F;       // using the 'const' keyword
    #define LENGTH 50               // using the '#define' directive
    #define AREA (LENGTH * WIDTH)    // macro with an expression

    C Constant Value Usage

    Constants can be utilized in various programming elements, including expressions, arrays, function parameters, and structures. Employing constants in programming constructs ensures consistent behavior, improves code readability, and maintains data integrity by safeguarding against unintentional modifications.

    Constant expressions in C

    A constant expression evaluates to a constant value entirely during the compilation process. Constant expressions can include integer, floating-point, or character constants, as well as enumeration constants and certain function calls. They are used in the following situations:

    • Defining array sizes for static or global arrays
    • Declaring case labels in switch statements
    • Specifying values for enumerators
    • Setting constant function arguments

    Examples of constant expressions:

    const int ARR_SIZE = 50;           // array size
    int values[ARR_SIZE];              // static array
    switch (grade) {
      case 'A':                        // case label
        // code

    Enumeration constants in C

    Enumeration constants are symbolic names assigned to a set of integer constant values. Enumerations are user-defined data types used to represent a collection of related values in a more readable and self-explanatory manner. They are declared using the 'enum' keyword, followed by the enumeration name, and the enumerator list enclosed within curly braces. Each enumerator in the list is assigned a unique integer value, starting from 0 by default and incrementing by 1 for each subsequent enumerator. However, you can explicitly specify integer values for enumerators as needed.

    enum enumeration_name {
      enumerator1 [= value1],
      enumerator2 [= value2],

    Enumeration constants can be used in various constructs, such as switch statements, conditional expressions, and looping statements. In addition, they can be used as arguments for functions that expect integer values.

    Example of enumeration constants:

    enum Days {
      SUNDAY,    // 0
      MONDAY,    // 1
      TUESDAY,   // 2
      WEDNESDAY, // 3
      THURSDAY,  // 4
      FRIDAY,    // 5
      SATURDAY   // 6
    int main() {
      enum Days today;
      today = WEDNESDAY;
      // ...

    C Constant Examples and Applications

    Using constants in C programs can help prevent errors and improve the code's maintainability. In the following example, we will use constants to calculate the area of a circle:

    const float PI = 3.14159;
    int main() {
      float radius, area;
      printf("Enter radius: ");
      scanf("%f", &radius);
      area = PI * radius * radius;
      printf("Area of the circle is: %.2f\n", area);
      return 0;

    In this example, we define the constant 'PI' as a floating-point value representing the mathematical constant π. The value of PI remains constant throughout the program and cannot be modified. By using the constant, we eliminate the risk of inadvertently altering the value of PI, leading to incorrect results or inconsistent behavior. The program then calculates the area of the circle using the constant PI and the user-provided radius.

    C Constant Array

    A constant array in C is an array whose elements cannot be modified. You can create a constant array by declaring it with the 'const' keyword, signifying that its contents should remain constant throughout the program. Here is an example of declaring a constant array in C:

    const char DAYS_OF_WEEK[7][10] = {
    int main() {
      for (int i = 0; i < 7; i++) {
        printf("%s\n", DAYS_OF_WEEK[i]);
      return 0;

    In this example, we define a constant two-dimensional character array 'DAYS_OF_WEEK', which contains the names of the days of the week. The array is marked as constant using the 'const' keyword, indicating that its elements cannot be modified throughout the program's execution.

    Modify a constant array in C (possible or not?)

    Attempting to modify a constant array in C will lead to compilation errors, as constants are meant to remain immutable throughout the program's execution. If you attempt to modify a constant array, the compiler will raise an error, alerting you to the violation of constancy. The following example demonstrates what happens when you attempt to modify a constant array:

    const int NUMBERS[5] = { 1, 2, 3, 4, 5 };
    int main() {
      // Attempt to modify a constant array
      NUMBERS[0] = 10; // This line will cause a compilation error
      return 0;

    When attempting to compile the above code, the compiler will generate an error message due to the attempted modification of the constant array 'NUMBERS'. The error message will indicate that you cannot assign a new value to an element of a constant array.

    C Constant Pointer

    A constant pointer in C is a pointer that cannot change the address it points to once assigned. You can create a constant pointer by using the 'const' keyword with the pointer declaration and placing it after the data type. The syntax for declaring a constant pointer is:

    data_type *const pointer_name = memory_address;

    Declaring a constant pointer ensures that the address it points to remains immutable throughout the program's execution. Here is an example of declaring and using a constant pointer in C:

    int main() {
      int num = 42;
      int const *ptr = #
      printf("Value at address %p is %d\n", ptr, *ptr);
      // The following line would result in a compilation error
      // ptr = &another_variable;
      return 0;

    Use a constant pointer in C

    Once declared and assigned to a memory address, a constant pointer cannot be changed to point to a different address. However, the value at the pointed address can still be changed. This is useful when you want to ensure that the pointer always points to the intended address and avoids inadvertently assigning it to a different memory location. Here is an example of using a constant pointer in C:

    int main() {
      int num = 42;
      int another_variable = 99;
      int *const ptr = #
      printf("Value at address %p is %d\n", ptr, *ptr);
      // The following line will NOT result in a compilation error
      num = 100;
      printf("Updated value at address %p is %d\n", ptr, *ptr);
      // However, this line would result in a compilation error:
      // ptr = &another_variable;
      return 0;

    In this example, we have a pointer 'ptr', which points to the address of variable 'num'. After declaring the pointer as constant, we can still update the value of 'num', but we cannot change the address that 'ptr' points to. If we try to update the address, the compiler will generate an error message.

    C Constant - Key takeaways

    • C Constant: A value that remains unchanged during the execution of a program.

    • Types of C constants: Integer constants, Floating-point constants, and Character constants.

    • Defining a constant in C: Use the 'const' keyword or '#define' directive.

    • Constant expressions: Evaluate to a constant value during compilation and are used in various programming constructs.

    • Constant arrays and pointers: Immutable elements or addresses that improve code maintainability and prevent errors.

    Frequently Asked Questions about C Constant
    What is the value of the constant C?
    The value of C constant, which represents the speed of light in a vacuum, is approximately 299,792,458 metres per second (m/s). This constant is often symbolised by "c" in scientific equations and is considered a fundamental constant of nature.
    How can I insert a constant in C?
    To put a constant in C, use the `const` keyword before the data type and variable declaration. For example, `const int myConstant = 10;`. This creates a constant integer with the value 10, and its value cannot be changed throughout the program. The identifier's name in capital letters (e.g., MY_CONSTANT) is a common naming convention for constants.
    Why is there a constant C?
    A constant 'C' is used in programming to provide a fixed value that cannot be changed or modified throughout the program. This maintains consistency and ensures specific values remain constant, reducing the chances of errors or unintended behaviour during the execution of the program. Constants enhance code readability, making it easier for programmers to understand the meaning and purpose behind the values. Finally, using constants in a program can help optimise memory usage and improve the overall efficiency of the code.
    Why is there a constant C?
    Constants, like 'C', are used in programming to define values that remain unchanged throughout the program's execution. Constants provide readability, maintainability, and help prevent accidental changes to the values they represent. Using constants ensures that any alterations to these values only need to be made in a single place, reducing the risk of errors and inconsistencies in the code.
    What are static and constant in C?
    In C, 'static' is a storage class specifier that grants a variable or function internal linkage, limiting its scope to the current source file and preserving its value across function calls. 'Constant' refers to a value or variable whose content cannot be changed after its initial declaration, ensuring that the value remains fixed throughout the program's execution.

    Test your knowledge with multiple choice flashcards

    What can be modified after declaring a constant pointer in C?

    How is a constant array declared in C?

    How are enumeration constants in C declared and assigned values?


    Discover learning materials with the free StudySmarter app

    Sign up for free
    About StudySmarter

    StudySmarter is a globally recognized educational technology company, offering a holistic learning platform designed for students of all ages and educational levels. Our platform provides learning support for a wide range of subjects, including STEM, Social Sciences, and Languages and also helps students to successfully master various tests and exams worldwide, such as GCSE, A Level, SAT, ACT, Abitur, and more. We offer an extensive library of learning materials, including interactive flashcards, comprehensive textbook solutions, and detailed explanations. The cutting-edge technology and tools we provide help students create their own learning materials. StudySmarter’s content is not only expert-verified but also regularly updated to ensure accuracy and relevance.

    Learn more
    StudySmarter Editorial Team

    Team Computer Science Teachers

    • 10 minutes reading time
    • Checked by StudySmarter Editorial Team
    Save Explanation Save Explanation

    Study anywhere. Anytime.Across all devices.

    Sign-up for free

    Sign up to highlight and take notes. It’s 100% free.

    Join over 22 million students in learning with our StudySmarter App

    The first learning app that truly has everything you need to ace your exams in one place

    • Flashcards & Quizzes
    • AI Study Assistant
    • Study Planner
    • Mock-Exams
    • Smart Note-Taking
    Join over 22 million students in learning with our StudySmarter App
    Sign up with Email

    Get unlimited access with a free StudySmarter account.

    • Instant access to millions of learning materials.
    • Flashcards, notes, mock-exams, AI tools and more.
    • Everything you need to ace your exams.
    Second Popup Banner