Editing C syntax (section)

===Syntax===
A C function definition consists of a [[return type]] ({{code|void}} if no value is returned), a unique name, a list of parameters in parentheses, and various statements:
<syntaxhighlight lang=C>
<return-type> functionName( <parameter-list> )
{
    <statements>
    return <expression of type return-type>;
}
</syntaxhighlight>

A function with non-{{code|void}} return type should include at least one {{code|return}} statement. The parameters are given by the {{code|<parameter-list>}}, a comma-separated list of parameter declarations, each item in the list being a data type followed by an identifier: {{code|<data-type> <variable-identifier>, <data-type> <variable-identifier>, ...}}.

The return type cannot be an array type or function type.
<syntaxhighlight lang=C>
int f()[3];    // Error: function returning an array
int (*g())[3]; // OK: function returning a pointer to an array.

void h()();    // Error: function returning a function
void (*k())(); // OK: function returning a function pointer
</syntaxhighlight>

If there are no parameters, the {{code|<parameter-list>}} may be left empty or optionally be specified with the single word {{code|void}}.

It is possible to define a function as taking a variable number of parameters by providing the {{code|...}} keyword as the last parameter instead of a data type ad variable identifier. A commonly used function that does this is the standard library function {{code|printf}}, which has the declaration:
<syntaxhighlight lang=C>
int printf (const char*, ...);
</syntaxhighlight>

Manipulation of these parameters can be done by using the routines in the standard library header [[stdarg.h|{{code|<stdarg.h>}}]].

====Function Pointers====
A pointer to a function can be declared as follows:
<syntaxhighlight lang=C>
<return-type> (*<function-name>)(<parameter-list>);
</syntaxhighlight>

The following program shows use of a [[function pointer]] for selecting between addition and subtraction:
<syntaxhighlight lang=C>
#include <stdio.h>

int (*operation)(int x, int y);

int add(int x, int y)
{
    return x + y;
}

int subtract(int x, int y)
{
    return x - y;
}

int main(int argc, char* args[])
{
   int  foo = 1, bar = 1;

   operation = add;
   printf("%d + %d = %d\n", foo, bar, operation(foo, bar));
   operation = subtract;
   printf("%d - %d = %d\n", foo, bar, operation(foo, bar));
   return 0;
}
</syntaxhighlight>