C++ Variables and File Handling

Basic Variable Types:

• Integral Classes
• char (single characters, such as 'T', 'x', or '9'. Use single quotes)
• short (short integers)
• int (medium-sized integers)
• long int (long integers)

Note: You can use the keyword 'unsigned' before any of the above to restrict the class to hold only positive integer values.

• Floating point classes
• float (real numbers that allow scientific notation)
• double (real numbers with greater precision than 'float')
• long double (real numbers with greater precision than 'double')
• Strings Such as "Hello world". In order to use strings, you must type #include "cstring.h" at the beginning of your program

Math Operators

• addition: +
• subtraction: -
• multiplication: *
• division: /
• modules: %
• assignment: =

Order of operations: Expressions in brackets are evaluated first. The operators *, /, and % are evaluated from left to right in the order they appear. After that, + and - are evaluated from left to right.

Declaring Variables:

<class> <variable name>;

Or, to assign a value to assign a value to the variable right away, you can type

<class> <variable name> = <initial value>;

For example,

int ab = 5;
unsigned long int cd = 3948293;
float answer;

Input and Output

If you want to write a value to the screen, just type

cout << <value>;

To start a new line, type cout << endl;

You can combine these two, along with variables.

For example,

cout << "You are " << age << " years old." << endl;

To read a variable in, type cin >> <variable>;

To use input and output in your programs, you must type

#include <iostream.h>

at the beginning of your programs.

Input and output with files

Do use input and output with files, you must type

#include <iostream.h>

at the beginning of your programs.

You must first declare a variable to open a file.

To do this, type ofstream MyFile; (or any value you want for 'MyFile'). Then, you can perform operations with it.

For example,

MyFile.Open ("c:\testfile.txt");

After that, you can output to the file just as you would output to the screen, except you type the value of the file first.

For example,

MyFile << "Line one of output" << endl;

When you're finished writing to the file, you must close it. To do this, type MyFile.close();

Reading from a file is just as easy. You must declare an input file as 'ifstream'.

For example,

ifstream MyFile ("textfile.txt");
MyFile >> a;
MyFile >> b;
cout << "the file contained the values " << a << " and " <<
b << endl;
MyFile.close()

You can read and write to the same file, but make sure you don't do it at the same time. You must close between operations.