C++ Tutorial
The basics of C and C++ are pretty easy to learn. C and C++ are compiled languages. C++ is nearly a superset of C. I'll concentrate on C++. Free compilers are available for C++ on all platforms. C++ is everywhere.
Linux:
- gcc from gnu
- gcc from gnu
- Microsoft CL compiler (yes it's free!) open source competition is great isn't it! (You can also get the .net toolkit, for free, which gives you the C# compiler.)
lesson1.cpp
int main()
{
// I don't do anything...
/*
no, not anything, at all.
*/
}
{
// I don't do anything...
/*
no, not anything, at all.
*/
}
The program comments say it all; this program doesn't do anything, but it does compile! And it compiles without errors or warnings. It also illustrates the general structure of a C++ program.
- The main() function is the mandatory function for all C++ programs.
- All functions require a return type, and main requires an int return type.
- The main() function also has a variety of input variable formats that you could place in the ( ) braces.
- The squiggly braces { and } denote the opening and closing of the scope.
- For a function declaration like main, they denote the beginning and ending of the function code. (More on this later.)
How to compile the thing? Assuming Linux and g++, (the C++ compiler flavor of gcc from gnu), at the command line you would just type:
g++ lesson1.cpp
at the command line. The result, in notoriously POSIX fashion, is the cryptically named executable a.out.
If you want to instead name the file something more reasonable, like lesson1, you would type
g++ lesson1.cpp -o lesson1
Getting back to the program code, both types of C++ comments are shown.
- Use two forward slashes '//' To add a comment that ends naturally at a linefeed.
- To add a block of comment, start with '/*' and end with '*/'.
You are qualified! If you have transcribed the lesson 1 code and compiled it, feel free to put down C++ as one of your skills on your resume. (Just kidding! Theres a little more work to do.)
lesson2.cpp
// lesson2.cpp
#include <iostream>
#include <iomanip>
// very important unless you like to type a lot
using namespace std;
int main( int ac, char ** av)
{
int i;
cout << "ASCII TABLE" << endl;
for( i=0; i<256; i++)
{
cout << " int [" << dec << ((int) i) << "]";
cout << " hex [" << hex << ((int) i) << "]" << " = [";
if( i != 27 )
{
cout << ((char) i);
}
else
{
cout << "the escape character!";
}
cout << "]" << endl;
}
return 0;
}
#include <iostream>
#include <iomanip>
// very important unless you like to type a lot
using namespace std;
int main( int ac, char ** av)
{
int i;
cout << "ASCII TABLE" << endl;
for( i=0; i<256; i++)
{
cout << " int [" << dec << ((int) i) << "]";
cout << " hex [" << hex << ((int) i) << "]" << " = [";
if( i != 27 )
{
cout << ((char) i);
}
else
{
cout << "the escape character!";
}
cout << "]" << endl;
}
return 0;
}
Lesson 2 actually does something useful.
It prints out the ascii character set from 0 to 255.
Lesson 2 introduces the concept of streams.
To compile lesson 2, lets change the command a little to:
g++ -pedantic lesson2.cpp -o lesson2
Can you guess what the -pedantic does? Pedantic is like -WAll, detailed warnings about stuff in your code. While your learning, (and even when your not, it's a good idea to include -pedantic or -Wall in your compile statement. Now, starting from the top...
At the top of the file is an ANSI C comment line:
// lesson2.cpp
The compiler ignores anything between the // sequence and a newline character.
The next significant lines in the program are:
#include <iostream>
#include <iomanip>
These are interpreted by the C++ pre-processor. Whats a preprocessor? C++ is compiled in multiple passes (at least two.) The preprocessor is called first to fixup the program code in the ways specified by pre-processor directives. '#include' is one such. It tells the pre-processor to go find the requested file and add it to the program code at the point of the directive statement.
iostream and iomanip are two include files that have definitions of the io streams and io manipulators that are nearly vital to C++. Lesson 2 has examples of the use of these.
Next comes the following:
// very important unless you like to type a lot
using namespace std;
The 'using namespace' directive tells the compiler that you want to reference class and entitiy names directly without having to prefix everything with the entities namespace. The C++ standard library, including streams and templates is in the namespace 'std' (for 'standard, not sexually transmitted diseases!) Namespaces were added to the C++ standard in order to prevent the 'name collision' that results when using different libraries that may use the same class names for different classes.
int main( int ac, char ** av)
This is the entry point to the mandatory main function. As written in lesson one, there are alternative argument lists to main. This is the fairly typical one.
int i;
Declare an instance of i, of type integer.
One of the native types, ex:( int, short, long long long, float, double, long double, char, wchar).
Now for the magic:
cout << "ASCII TABLE" << endl;
No other language has this symantic concept (maybe 'D'?).
There are three standard streams for all C++ programs...
- cin - the input stream
- cout - standard output
- cerr - error output
The << characters sequence is the stream output operator.
It outputs the character string "ASCII TABLE" to standard output.
The 'endl' thing is a 'stream manipulator'.
It puts the proper end of line termination into the stream. On MSDOS, OS/2 and Windows, the proper end of line is 'CRLF'. On Unix and Linux, it is 'LF'.
Streams make for a lightweight way of moving stuff to and from 'files'. In Unix/Linux standard input and output and error are open files to the console (typically).
for( i=0; i<256; i++)
{
}
This construct is a 'for loop'. It iterates through a sequence until a condition is no longer true.
The for statement is really three statements...
for( i=0; i<256; i++) The highlighted initializes things. It's executed at the start of the iteration.
for( i=0; i<256; i++) The highlighted is the test condition.
If false, the program falls out of the loop; after the closing brace.
The 'test' is executed before statements in the braces.
for( i=0; i<256; i++) The highlighted increments the variable i by 1.
It's executed last, after statements in the braces.
More coming later...