1. What Is? function predefined, programmer-defined
arguments, (formal) parameters
return value
function call, function invocation
function definition
head, body
function prototype (declaration)
expanded form, abbreviated form
local variables, global variables, scope
call-by-value

2. Programming in Multiple Files2

3. (Non) Executable Statements
all C++ statements are divided into executable and non-executable
executable - some corresponding machine code is generated by the compiler
examples: assignment statements, looping/branching constructs, function invocations
non-executable - no machine code generated
examples: function prototypes, global variable and constant declarations, #include directives
global constant declarations may look like executable – but they are not:
const double PI=3.14;
the compiler substitutes 3.14 for every occurrence of PI in the program

4. Include Files
#include instructions tell the compiler to include a specified file. The files included are also called header files and commonly have extensions .h
two forms:
#include <filename> - the file is found in a standard system-dependent location
#include ”filename.h” - the file is located in the same directory as the rest of the code
the include directives are processed before the rest of the compilation
include files may also contain include directives
what to put in include files - non-executable statements
what not to put in include files - executable statements, function definitions
purpose of include files - centralize declarations

5. Program in Multiple Files
large programs are usually kept in multiple files
reasons:
easy to maintain
can be compiled separately
functions are usually grouped into files by their purpose (functions dealing with one particular part of program are kept in one file)
function invocations, constants and variables cannot be put in program before the corresponding declarations.
what if they are in a separate file?
program is structured as follows:
program file (extension .cpp) - contains function definitions
include file (extension .h) - contains corresponding function prototypes, global constant and variable declarations
if function A defined in file AA.cpp needs to call a function B which is defined in a different file BB.cpp - the corresponding header file BB.h is included in file AA.cpp

6. Example Program in Multiple Files
#include "add1.h"
// adds 1,
// returns added value
int add1(int n) {
return (n + 1); }
add1.cpp
add1.h
// adds one
int add1(int);
// uses the function add1
// defined in a separate file
#include <iostream>
#include "add1.h"
int main() {
// get the number
cout << "Enter a number: ";
int n;
cin >> n;
// find the number plus 1
int newn = add1(n);
// print out the number plus 1
cout << newn << endl; }
add1test.cpp

7. Separate Compilation Separate compilations Source program (add1.cpp)
Include files (add1.h, iostream)
Link object file
with standard
object files
and other
object files to
produce an
executable
program
Add include files
Check
Object file (add1.o)
file
unit for legal
syntax and
compile it into
an object file
Standard libraries
compilation
Executable program

8. Preprocessor Directives
each definition (e.g. global constant def.) can be encountered only once during compilation
when definition is placed in a header file, it may be included multiple times
header file must structured so it is safe in case of multiple inclusion; term – multiple inclusion protection
mechanism - preprocessor directives
#define name value note that substitution is textual
problem: #define press 50
(later)
int press=20;
The name in the declaration gets substituted, creating a syntax error.
#ifdef name - true if name defined, #ifndef name - true if not
#endif - completes #if
header file myheader.h containing definitions usually has the following structure:
#ifndef MYHEADER_H
#define MYHEADER_H
// text of the header file goes here
#endif