Basic Elements of C++ (III)
Basic Elements of C++ (III)
Preprocessor Directives
• Only a small number of operations, such as arithmetic and assignment operations, are explicitly defined in C++.
• Many of the functions and symbols needed to run a C++ program are provided as a collection of libraries. For example, in order to perform input/output, the header file iostream must be included.
• Preprocessor directives and the names of header files to tell the computer the locations of the code provided in libraries.
• Preprocessor directives are processed by a program called a preprocessor.
• All preprocessor commands begin with #. There are no semicolons at the end of the preprocessor commands and they appear as the first line of a program.
• The general syntax is # include
• The preprocessor commands are processed by the preprocessor before the program goes through the compiler.
Commonly used header files are
| |input/output |
| |math functions |
| |string functions |
| |formatting manipulations for input/output |
Creating a C++ Program
• Using the proper structure for a C++ program makes it easier to understand and subsequently modify the program.
• Every C++ program is divided into two parts: the preprocessor directives and the program. Taken together, the preprocessor directives and program statements constitute the C++ source code.
• To be useful, this source code must be saved in a file that has the file extension .cpp.
• Compiler generates the object code
− Saved in a file with file extension .obj
• Executable code is produced and saved in a file with the file extension .exe.
Program Style and Form
• Every C++ program has a function main
• Basic parts of function main are:
− The heading
− The body of the function
1) The heading part
The heading part has the following form:
typeOfFunction main(argument list)
2) The body of the function
➢ The body of the function is enclosed between { and }
➢ Has two types of statements
• Declaration statements
✓ int a, b, c;
✓ double x, y;
• Executable statements. Three forms:
✓ a = 4; //assignment statement
✓ cin>>b; //input statement
✓ cout ................
................
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