Simple C Program

#include  <stdio.h>
int main ()
{
     printf ( “Hello, World!\n” ) ;
     return 0 ;
}

Program Header Comment and Preprocessor Directives

A comment is descriptive text used to help a reader of the program understand its content.

All comments must begin with the characters  /*  and end with the characters  */

These are called comment delimiters

The program header comment always comes first.

Lines that begin with a # in column 1 are called preprocessor directives (commands).

Example:  the #include <stdio.h> directive causes the preprocessor to include a copy of the standard input/output header file stdio.h at this point in the code.

This header file was included because it contains information about the printf ( ) function that is used in this 

program.

C Standard Library

Every implementation of C comes with a standard library of predefined functions.

Note that, in programming, a library is a collection of functions.

The functions that are common to all versions of C are known as the C Standard Library.

Function Name	Math Name	Value	Example
abs(x)	absolute value	|x|	abs(-1)	returns	1
sqrt(x)	square root	x0.5	sqrt(2.0)	returns	1.414…
exp(x)	exponential	ex	exp(1.0)	returns	2.718…
log(x)	natural logarithm	ln x	log(2.718…)	returns	1.0
log10(x)	common logarithm	log x	log10(100.0)	returns	2.0
sin(x)	sine	sin x	sin(3.14…)	returns	0.0
cos(x)	cosine	cos x	cos(3.14…)	returns	-1.0
tan(x)	tangent	tan x	tan(3.14…)	returns	0.0
ceil(x)	ceiling	┌ x ┐	ceil(2.5)	returns	3.0
floor(x)	floor	└ x ┘	floor(2.5)	returns	2.0