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In most programming languages, functions may take one or more arguments. Usually, each argument must be specified in full (this is the case in the C programming language [1]). Later languages (for example, in C++) allow the programmer to specify default arguments that always have a value, even if one is not specified when calling the function.
In most of today's popular programming languages and operating systems, a computer program usually only has a single entry point.. In C, C++, D, Zig, Rust and Kotlin programs this is a function named main; in Java it is a static method named main (although the class must be specified at the invocation time), and in C# it is a static method named Main.
A function definition starts with the name of the type of value that it returns or void to indicate that it does not return a value. This is followed by the function name, formal arguments in parentheses, and body lines in braces. In C++, a function declared in a class (as non-static) is called a member function or method.
The main function serves a special purpose in C programs; the run-time environment calls the main function to begin program execution. The type specifier int indicates that the value returned to the invoker (in this case the run-time environment) as a result of evaluating the main function, is an integer. The keyword void as a parameter list ...
In case of call by value, what is passed to the function is the value of the argument – for example, f(2) and a = 2; f(a) are equivalent calls – while in call by reference, with a variable as argument, what is passed is a reference to that variable - even though the syntax for the function call could stay the same. [5]
Notice that the type of the result can be regarded as everything past the first supplied argument. This is a consequence of currying, which is made possible by Haskell's support for first-class functions; this function requires two inputs where one argument is supplied and the function is "curried" to produce a function for the argument not supplied.
An example of C argument parsing would be: #include <stdio.h> int main ... C also has functions called getopt and getopt_long. C#
getopt is a system dependent function, and its behavior depends on the implementation in the C library. Some custom implementations like gnulib are available, however. [6]The conventional (POSIX and BSD) handling is that the options end when the first non-option argument is encountered, and that getopt would return -1 to signal that.