Actual parameter

In computer science, an actual parameter is a name or value passed to a subroutine. This is not to be confused with a formal parameter, which is the name by which the subroutine refers actual parameter. For example, in C,

int foo(int a)
{
   int b = 5;

   return a + b;
}

int bar(void)
{
   return foo(1);
}

The subroutine bar() calls foo(). When bar() calls foo(), it passes the constant 1. Within bar(), 1 is an actual parameter to foo(). Within foo(), a is a formal parameter which references the actual parameter 1 from bar().