What does the word "literal" mean?

Question

A literal is "any notation for representing a value within source code" (wikipedia)

(Contrast this with identifiers, which refer to a value in memory.)

Examples:

• "hey" (a string)
• false (a boolean)
• 3.14 (a real number)
• [1,2,3] (a list of numbers)
• (x) => x*x (a function)
• /^1?$|^(11+?)\1+$/ (a regexp)

Some things that are not literals:

• std::cout (an identifier)
• foo = 0; (a statement)
• 1+2 (an expression)

A literal is a value that has been hard-coded directly into your source.

For example:

string x = "This is a literal";
int y = 2; // so is 2, but not y
int z = y + 4; // y and z are not literals, but 4 is
int a = 1 + 2; // 1 + 2 is not a literal (it is an expression), but 1 and 2 considered separately are literals

Some literals can have a special syntax, so you know what type the literal is:

//The 'M' in 10000000M means this is a decimal value, rather than int or double.
var accountBalance = 10000000M; 

What sets them apart from variables or resources is that the compiler can treat them as constants or perform certain optimizations with code where they are used, because it's certain they won't change.

A literal is an assignment to an explicit value, such as

int i = 4;  // i is assigned the literal value of '4'
int j = i   // j is assigned the value of i.  Since i is a variable,  
            //it can change and is not a 'literal'

EDIT: As pointed out, assignment itself has nothing to do with the definition of a literal, I was using assignment in my example, but a literal can also be passed into a method, etc.

A literal is when you include the value in the source code (as opposed to referencing a variable or a constant). For example:

int result = a + 5; // a is a variable with a value, 5 is a literal

string name = "Jeff Atwood"; // name is a variable initialized
                             // with the string literal, "Jeff Atwood"

int[] array = new int[] {1, 2, 3}; // C# has array literals (this is actually three
                                   // int literals within an array literal)

If the literal represents some quantity, like a physical constant, it's better to give it a name instead of writing the same literal everywhere you need it. That way, when you are reading the source code, you know what the number means, which is usually more important than its value (which could change anyways).

const int maxUsers = 100;
const double gravitationalAcceleration = 9.8;

Generally, the only numeric literals I use (besides to initialize constants like above) are 0 or 1, and sometimes 2 if I'm skipping every other item in a loop. If the meaning of the number is more important than its actual value (it usually is), its better to name it.

A literal value is a value, but a value could also be stored in a variable. In the statement

string str = "string literal";

there's a string variable (str) and a string literal. After the statement is executed they both have the same value.

Be aware that in many languages the variable and the literal value don't necessarily even have to be the same type. For example:

int a = 1.0;

The literal value above is a floating point type. The value will be coerced by the compiler to fit into the int variable.

For another example, in the first line of C++ code above the type of a string literal isn't actually the library type string at all. To maintain backwards compatibility with C, string literals in C++ are char arrays.

Quick example:

int my_int_var = 723;

723 - This set of characters refers to a literal integer value.

my_int_var - This set of characters refers to a variable integer value.

A literal is when you put it in the code. So a string literal is

string s = "SomeText";

This is as opposed to building the string, or taking it in as a parameter.