A constant is a value or variable that can't be changed in the program, for example, 10, 20, 'a', 3.4, "c programming" etc.

A constant is a named memory location in a program that holds a single value throughout the execution of that program. It can be of any data type- character, floating-point, string, double, integer, etc. There are various types of constants in C. It has two major categories- primary and secondary constants. Character constants, real constants, integer constants, etc., are types of primary constants. Structure, array, pointer, union, etc., are types of secondary constants.

It can be an octal integer or a decimal integer or even a hexadecimal integer. We specify a decimal integer value as a direct integer value, while we prefix the octal integer values with ‘o’. We also prefix the hexadecimal integer values with ‘0x’.

The integer constant used in a program can also be of an unsigned type or a long type. We suffix the unsigned constant value with ‘u’ and we suffix the long integer constant value with ‘l’. Also, we suffix the unsigned long integer constant value using ‘ul’.

Floating Point Constants / Real Constants

This type of constant must contain both the parts- decimal as well as integers. Sometimes, the floating-point constant may also contain the exponential part. In such a case when the floating-point constant gets represented in an exponential form, its value must be suffixed using ‘E’ or ‘e’.

We represent the floating-point value 3.14 as 3E-14 in its exponent form.

The character constants are symbols that are enclosed in one single quotation. The maximum length of a character quotation is of one character only.

Some predefined character constants exist in the C programming language, known as escape sequences. Each escape sequence consists of a special functionality of its own, and each of these sequences gets prefixed with a ‘/’ symbol. We use these escape sequences in output functions known as ‘printf()’.

The string constants are a collection of various special symbols, digits, characters, and escape sequences that get enclosed in double quotations.

The definition of a string constant occurs in a single line:

We can define this with the use of constant multiple lines as well:

The definition of the same string constant can also occur using white spaces:

All the three mentioned above define the very same string constant.

Generally, in the C programming language, constants are assigned with some value and this value is known as literal. Hence in the C programming language constants are also known as literals.

Here “100” is constant integer literal in the above constant expression.

We should be careful while defining the constants, as just using the “const” keyword and declaring is as simple as declaring the variables in C. But declaration should be done as

The below two declarations are not valid for defining the constants:

For the declaration of constants, it is always the best practice for writing constant names in capital letters or uppercase letters. This helps in understanding and readable program to others as well as for us.

We cannot change the value of the constant once assigned using the “const” keyword or #define directive, because it will give an error if try to assign some other value to the constant that is declared.

In this article, we have discussed the constants in the C programming language. The constants are divided into two categories primary and secondary constants in which primary constants consist of numerical constants like integer, decimal, real, etc, and character constants like character, string, backslash, etc. In secondary constants, we have an array, pointer, structure, union, etc. Constants in C are those whose values cannot be altered once declared and these constants are also known as literals.

In this blog, we'll know about the constants in C.

What  Are The Constants In C?

A constant pointer in C cannot change the address of the variable to which it is pointing, i.e., the address will remain constant. Therefore, we can say that if a constant pointer is pointing to some variable, then it cannot point to any other variable.

<type of pointer> *const <name of pointer>;  

The Declaration of a constant pointer is given below:

We can explain the working of the constant pointer in the following way, 

const int * ptr, Then writing the const means we're informing the compiler about the ptr variable. We're informing them that this is a variable that will hold the address of a variable integer. 

If we try to change the value refocused by the pointer it'll throw an error. Simply we can't change the value refocused by it but we can change the pointer. 

To change the pointer itself we can assign it in this way “ ptr = & variable1”. Then we're changing the pointer itself. 

Still, it'll not work as we're trying to change the value refocused by the pointer, If we try to write it * ptr = variable1. 

To produce any constant pointer the first thing which we need is the data type of the pointer. This informs the C compiler about the data type of the variable which pointer is going to hold. We can define housekeeper, int, pier according to our demand. 

The alternate important trait of any constant pointer is the keyword const. This trait is used to inform the C compiler about the variable geste which we're going to use in the program. This informs the compiler that whatever variable address it'll hold. And it notifies the C compiler that whatever it'll hold will remain the same for the rest of the program. In case we try to change the pointer value it'll throw an error. 

A third important trait of the constant pointer is the Any name of pointer. This trait is the name of the pointer which is going to point to the variable address. If we publish the printer “ * pointer” name will show us the address of the pointing variable. 

A fourth important trait of the constant pointer is the *. Then * represents the value of the variable held by the pointer. 

Here are the following examples mentioned below:

In this example, we are defining a constant pointer and changing the variable pointed by it.

We are writing code inside the main, where we have defined a few variables like variable1 and variable2 and we defined a const char pointer.

The variable1 address will be pointed by the const char pointer variable.

Finally, we are printing data into two formats, one with a pointer holding the address of the variable1 and the next after changing the allocation of the pointer.

In the last print, we can see the pointer is pointing to variable2.

Please see the below example along with the screen of output

//*pointer = variable2; This is not the correct way to change the pointer value , it will throw an error.

// Still we can change the pointer by changing the pointer itself

printf( "Current value of the pointer is : %c\n", *pointer);

printf( "The value of the pointer after change is : %c\n", *pointer);

In this example, we are shown how we are changing the variable pointed by the pointer and even after changing the variable pointed by it still the pointer holds the same memory address.

Please see the below example along with the screen of output.

//*pointer = variable2; This is not the correct way to change the pointer address , it will throw an error.

printf( "The value pointed by the pointer is : %c\n", *pointer);

printf( "The address pointed by the char pointer is : %d\n\n", pointer);

// We are only changing the variable point by pointer it address still same

printf( "The address pointed by the char pointer is : %d\n", pointer);

From this tutorial, we learned about the const pointers in C programming and we learned about the const pointer’s actions with some important exemplifications. We learned the places where These const pointers can be used in real life with the help of some important exemplifications. 

In this article, you'll know about constant pointers in C.

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