C++ Constants/Literals and Modifier Types

C++ Constants/Literals

Constants refer to fixed values that the program may not alter and they are called literals.

Constants can be of any of the basic data types and can be divided into Integer Numerals, Floating-Point Numerals, Characters, Strings and Boolean Values.

Again, constants are treated just like regular variables except that their values cannot be modified after their definition.

Integer literals:

An integer literal can be a decimal, octal, or hexadecimal constant. A prefix specifies the base or radix: 0x or 0X for hexadecimal, 0 for octal, and nothing for decimal.

An integer literal can also have a suffix that is a combination of U and L, for unsigned and long, respectively. The suffix can be uppercase or lowercase and can be in any order.

Here are some examples of integer literals:

212         // Legal
215u        // Legal
0xFeeL      // Legal
078         // Illegal: 8 is not an octal digit
032UU       // Illegal: cannot repeat a suffix

Following are other examples of various types of Integer literals:

85         // decimal
0213       // octal
0x4b       // hexadecimal
30         // int
30u        // unsigned int
30l        // long
30ul       // unsigned long

Floating-point literals:

A floating-point literal has an integer part, a decimal point, a fractional part, and an exponent part. You can represent floating point literals either in decimal form or exponential form.

While representing using decimal form, you must include the decimal point, the exponent, or both and while representing using exponential form, you must include the integer part, the fractional part, or both. The signed exponent is introduced by e or E.

Here are some examples of floating-point literals:

3.14159       // Legal
314159E-5L    // Legal
510E          // Illegal: incomplete exponent
210f          // Illegal: no decimal or exponent
.e55          // Illegal: missing integer or fraction

Boolean literals:

There are two Boolean literals and they are part of standard C++ keywords:

  • A value of true representing true.
  • A value of false representing false.

You should not consider the value of true equal to 1 and value of false equal to 0.

Character literals:

Character literals are enclosed in single quotes. If the literal begins with L (uppercase only), it is a wide character literal (e.g., L’x’) and should be stored in wchar_t type of variable . Otherwise, it is a narrow character literal (e.g., ‘x’) and can be stored in a simple variable ofchar type.

A character literal can be a plain character (e.g., ‘x’), an escape sequence (e.g., ‘\t’), or a universal character (e.g., ‘\u02C0’).

There are certain characters in C++ when they are preceded by a backslash they will have special meaning and they are used to represent like newline (\n) or tab (\t). Here, you have a list of some of such escape sequence codes:

Escape sequence Meaning
\\ \ character
\’ ‘ character
\” ” character
\? ? character
\a Alert or bell
\b Backspace
\f Form feed
\n Newline
\r Carriage return
\t Horizontal tab
\v Vertical tab
\ooo Octal number of one to three digits
\xhh . . . Hexadecimal number of one or more digits

Following is the example to show few escape sequence characters:

#include <iostream>
using namespace std;

int main()
   cout << "Hello\tWorld\n\n";
   return 0;

When the above code is compiled and executed, it produces the following result:

Hello   World

String literals:

String literals are enclosed in double quotes. A string contains characters that are similar to character literals: plain characters, escape sequences, and universal characters.

You can break a long line into multiple lines using string literals and separate them using whitespaces.

Here are some examples of string literals. All the three forms are identical strings.

"hello, dear"

"hello, \


"hello, " "d" "ear"

Defining Constants:

There are two simple ways in C++ to define constants:

  • Using #define preprocessor.
  • Using const keyword.

The #define Preprocessor:

Following is the form to use #define preprocessor to define a constant:

#define identifier value

Following example explains it in detail:

#include <iostream>
using namespace std;

#define LENGTH 10   
#define WIDTH  5
#define NEWLINE '\n'

int main()

   int area;  
   area = LENGTH * WIDTH;
   cout << area;
   cout << NEWLINE;
   return 0;

When the above code is compiled and executed, it produces the following result:


The const Keyword:

You can use const prefix to declare constants with a specific type as follows:

const type variable = value;

Following example explains it in detail:

#include <iostream>
using namespace std;

int main()
   const int  LENGTH = 10;
   const int  WIDTH  = 5;
   const char NEWLINE = '\n';
   int area;  
   area = LENGTH * WIDTH;
   cout << area;
   cout << NEWLINE;
   return 0;

When the above code is compiled and executed, it produces the following result:


Note that it is a good programming practice to define constants in CAPITALS.

C++  Modifier Types

C++ allows the char, int, and double data types to have modifiers preceding them. A modifier is used to alter the meaning of the base type so that it more precisely fits the needs of various situations.

The data type modifiers are listed here:

  • signed
  • unsigned
  • long
  • short

The modifiers signed, unsigned, long, and short can be applied to integer base types. In addition, signed and unsigned can be applied to char, and long can be applied to double.

The modifiers signed and unsigned can also be used as prefix to long or short modifiers. For example, unsigned long int.

C++ allows a shorthand notation for declaring unsigned, short, or long integers. You can simply use the word unsigned, short, or long, without the int. The int is implied. For example, the following two statements both declare unsigned integer variables.

unsigned x;
unsigned int y;

To understand the difference between the way that signed and unsigned integer modifiers are interpreted by C++, you should run the following short program:

#include <iostream>
using namespace std;
/* This program shows the difference between
 * signed and unsigned integers.
int main()
   short int i;           // a signed short integer
   short unsigned int j;  // an unsigned short integer

   j = 50000;

   i = j;
   cout << i << " " << j;

   return 0;

When this program is run, following is the output:

-15536 50000

The above result is because the bit pattern that represents 50,000 as a short unsigned integer is interpreted as -15,536 by a short.

Type Qualifiers in C++

The type qualifiers provide additional information about the variables they precede.

Qualifier Meaning
con st Objects of type const cannot be changed by your program during execution
volatile The modifier volatile tells the compiler that a variable’s value may be changed in ways not explicitly specified by the program.
restrict A pointer qualified by restrict is initially the only means by which the object it points to can be accessed. Only C99 adds a new type qualifier called restrict.