Constants in C++ | Literals in C++

In this article, we will learn about constants and literals in C++.

What are Constants in C++?

Constants are expressions whose values remain fixed. Once defined, we cannot change the value of a constant.

What are Literals in C++?

The fixed value assigned to a constant is called literal. For example, in constant expression const int x = 10; the value 10 is called constant integer literal.

Following are the types of literals:

1. Integer Literals in C++

An integer is a numeric literal that does not contain any fractional or exponential parts. Integer literals are expressed as:

a. Prefix

It specifies the base or radix. These are of four types: no prefix for decimal (base 10), 0 for octal (base 8), 0x or 0X for hexadecimal (base 16) and 0b or 0B for binary (base 2).

For example:

• Decimal: 97, 3, -62, etc.
• Octal: 04, 021, 0743, etc.
• Hexadecimal: 0x2, 0X4a, 0x56c, etc.
• Binary: 0b10, 0B1011, 0b110, etc.

b. Suffix

It represents the type, u or U for unsigned, l or L for long and combination of both.

For example:

• 42 //int requires no suffix
• 42u //unsigned int
• 42ul //unsigned long
• 42L //long
• 42ll //long long

2. Floating-point Literals in C++

Floating-point literals, which represent real numbers, have an integer part, a real component, a fractional component, and an exponential part. We can store it either in decimal or in exponential form.

We must remember that

• The decimal point, exponential part, or both must be included in the decimal form; otherwise, an error will occur.
• In the exponential form, the integer, fractional, or both parts must be included; otherwise, an error will occur.

Some examples of valid floating-point literals are 12.365, 2.67E-6, etc.

Some examples of invalid floating-point literals are 256E, 0.e34, etc.

3. Character Literals in C++

Character literals store a single character enclosed within a single quote. These have two representations:

• Normal or narrow character literal of char type. For example, ‘i’.
• Wide character literal of wchar_t type which begins with uppercase L. For example, L’i’.

There are various characters in C++ that have special meaning. These character literals are Escape Sequences. Following is a list of some escape sequences in C++.

Example to illustrate the use of escape sequences in C++

#include <iostream>
using namespace std;

int main() {
  cout<<"TechVidvan\nGoogle\n";
  cout<<"Tech\tVidvan";
  return 0;
}

Output

4. String Literals in C++

String literals store multiple characters enclosed in double quotes. They can also include special characters, escape sequences and whitespaces.

For example: “TechVidvan”, “Data Flair”, “Hello World!\n”, etc.

5. Boolean Literals in C++

These represent boolean values, which are of two types:

true: represents true value. We should not consider its value equal to int 1.

false: represents false value. We should not consider its value equal to int 0.

Defining Constants in C++

We can define a constant in one of the two ways,

1. Using const keyword

We can define a constant using const keyword as prefix.
Syntax:

const datatype name = value;

Example to define constants using const

#include <iostream>
using namespace std;

int main() {
  const int a = 10;       //integer literal = 10
  const float b = 50.74;      //floating point literal = 50.74
  const char newline = '\n';      //character literal = \n
  
  cout<<"Defined constants:"<<newline;
  cout<<a<<newline;
  cout<<b;
  return 0;
}

Output

Let’s try to modify value of a constant

#include <iostream>
using namespace std;

int main() {
  const int a = 10;
  a = 20;
  cout<<a;
  return 0;
}

Status Compilation error
Output

We get a compilation error that variable a is read-only.

2. Using #define preprocessor directive

We can use #define preprocessor directive to declare constants.
Syntax:

#define name value

Example to define constants using #define

#include <iostream>
using namespace std;

#define length 12.5
#define breadth 8
#define unit "m sq."

int main() {
  double area;
  area = length * breadth;
  cout<<area<<" "<<unit;
  return 0;
}

Output

Summary

In this article, we learnt what constants are. We talked about literals in C++. Literals can be of integer, floating-point, character, string or boolean type. There are two ways in which we can define constants. Using suitable examples, we learnt both these ways.