Introduction to C / C++ Programming
Libraries

Overview

There are many libraries full of functions available in C/C++, either standard libraries that come with most systems or special libraries that can either be purchased or obtained for free from third parties. ( You can even create your own libraries. )
This page lists some of the most commonly used libraries and some of the most commonly used functions in each one.
This is not intended to be a complete listing.
See Appendix A of "Engineering Problem Solving with C++" or most any other good C++ book for more details.

In order to use library functions, you must #include a header file that contains definitions for the functions ( and sometimes important constants ) in the library.
The subtopics listed below correspond to the #include required to use the libarary in a C++ program. So to use the math library, you would need to include a line that said "#include <cmath>" at the beginning of the program.
For a C program ( as opposed to C++ ), remove the letter C from the beginning of the library name, and add a ".h" at the end. So to use the math library in C, you would need to "#include <math.h>"

This library is used by essentially every C++ program.
No exact equivalent in C, but most C programs #include <stdio.h> for their I/O needs.
cin - Standard input, normally the keyboard.
cout - Standard output, normally the screen, used for program results.
cerr - Standard error, normally the screen, used for error messages and other non-results messages.
Operators << and >>, defined for basic types.
int get( char ); - Gets a single character from the input stream.
getline( c_string var, int max, [ char delimiter ] ); - Gets a complete line.
char peek( ); - Examines the next input char but does not remove it from the input stream.
putback( char ); - Puts a character back on the input stream.
put( char ); - Outputs a single char.
flush( ); - Flushes the output buffer.

The standard C library. Automatically #included by <iostream>, so normally does not need to be directly #included.
RAND_MAX - The maximum value produced by the rand( ) function.
int rand( void ); - Returns a ( pseudo ) random integer from 0 to RAND_MAX
- Requires the use of srand ( see below )
- ( double ) rand( ) / RAND_MAX will yield a random double precison number from 0.0 to 1.0 inclusive.
void srand( unsigned int );
- Initializes the random number generator.
- Should be called exactly once in a program, usually in main, and before any calls to rand( );
- Ex: srand( time( NULL )); - Initializes the random number generator using the time as a seed.
void exit( int ); - Immediate normal program termination.
void abort( void ); - Immediate abnormal program termination.
int abs( int ); - Absolute value
- long labs( long ); - Absolute value
- See also fabs under <cmath> below.
double atof( const char[ ] ); - Converts a string of numeric characters ( e.g."3.14159E17" ) into a double precision number
- atoi and atol convert strings to ints and longs respectively.
NULL - Zero, formatted properly for use as a pointer.

Required for most of the standard math functions
sin, cos, tan, asin, acos, atan - Standard trig funtions, with angles in radians.
- sinh, cosh, etc. - Hyperbolic trig functions.
int ceil( double ); - rounds down to the next integer towards infinity.
- int floor( double ); - rounds to next integer towards minus infinity.
double exp( double ); - exponential - e raised to a power.
- double log( double ); - Natural logarithm, base e.
- double log10( double ); - Common logarithm, base 10.
double sqrt( double ); - Square root.
double fabs( double ); - Absolute value for doubles.
double pow( double x, double y ); - Raises x to the y power.
- If y is either 2 or 3, then it is faster to multiply out the terms than to call pow.
- I.e. use X * X or X * X * X instead of pow( X, 2 ) or pow( X, 3 ).

Functions for examining and manipulating character types
boolean isdigit( char ); - Determines if a character is a numeric digit ( 0 - 9 )
char toupper( char ); - Converts a character to upper case.
many others

Defined limits for the current system, such as the maximum value of an int or a double.