C standard library functions

Standard library contains the
prepackaged functions which are used
while writing a ‘c’ program.

 This header file contains a number of pre-
defined/ library functions which performs
various mathematical calculations.
 To include math.h header file in program use
preprocessor directive-
#include< math.h >

 Modulus function calculates the remainder of
the division operation.
 In ‘c’ modulus function is applied on integer
numbers only by default.
 To apply modulus to floating point values we
use fmod , fmod l ,modf , modf l.
 Modf / modf l splits double/ long double
number into integer and fractional part
respectively.
 It stores the integer in ipart and returns the
fraction.

•Declaration :-
•Fmod , fmod l :-
double fmod (double x , double y);
long double fmod l(long double (x) , long double (y))
•Modf , modf l :-
double modf (double x , double *(ipart));
long double modf l(long double (x) , long double
*(ipart));

ARC FUNCTIONS
SIMPLE
FUNCTIONS
 acos
 asin
 atan
 atan2
 acosl
 asinl
 atanl
 atn2l
 cos
 sin
 tan

Declarations :-
• Real :-
1. doubleacos(double x);
2. doubleasin(double x);
3. doubleatan(double x);
4. doubleatan2(double x ,double y);
5. long double acosl(longdouble (x));
6. long double asinl(longdouble (x));
7. long double atanl(longdouble (x));
8. longdouble atan2l(longdouble(x), long double (y));
• Complex :-
1. Complex acos(complex x);
2. Complex asin(complex x);
3. complex atan(complex x);

Declarations :-
•Real :-
1. Double cos (double x);
2. Double sin (double x);
3. Double tan (double x);
4. Longdouble cos (long double x);
5. Longdouble sin (long double x);
6. Longdouble tan (long double x);
• Complex :-
1. Complex cos (complex x);
2. Complex sin (complex x);
3. complex tan (complex x);

 cosh
 sinh
 tanh
 coshl
 sinhl
 tanhl

Declarations :-
• Real :-
1. Double cosh (double x );
2. Double sinh (double x);
3. Double tanh (double x);
4. Long double coshl (long double x);
5. Long double sinhl (long double x);
6. Long double tanh (long double x);
• Complex :-
1. Complex cosh (complex x);
2. Complex sinh (complex x);
3. Complex tanh (complex x);

power function calculates the power of an input
number.
Syntax :-
power( base , exponent);

TO CALCULATE
POWER OF A
‘DESIRED’ NUMBER
TO CALCULATE
POWER OF ‘10’
 pow
 powl
 Pow10
 Pow10 l

Declaration :-
•Power :-
1. Double pow (double n , double p );
2. Long double pow (long double (n) , long double (p
3. Complex pow (complex n , complex p);
4. Complex pow (double n , complex p);
5. Complex pow (complex n , double p);
• Power10 :-
1. Double pow10 (int p);
2. Long double pow10 (int (p));

 Floor function rounds the value down.
 Floor returns integer found as double.
 Floorl returns integer found as long double.
 Declaration :-
double floor (double x);
long double floorl(long double (x));

 Ceiling function rounds up a number.
 Ceil returns an integer found as double.
 Ceill returns an integer found as long double.
Declaration :-
double ceil (double x);
long double ceil (long double (x));

 Exponential function is used to calculate the
powers of ‘e’.
 For Real numbers ‘e’ raised to power ‘x’ is
calculated.
 For complex numbers ‘e’ raised to power ‘z’ is
calculated (z is a complex number).

Declaration :-
• Real :-
1. double exp(double x);
2. long double exp (long double (x));
•Complex :-
1. complex exp(complex (z));

 square root function is used to calculate the
square root of a given number.
 Declaration :-
 Real :-
double sqrt (double x);
long double sqrt (long double (x));
 Complex :-
complex sqrt (complex x);

 absolute value function returns only the numerical
value without any sign.
 There are different types of abs function :-
o abs (a macro) finds absolute value of an integer .
o fabs , fabs l (macros) finds absolute values of
floating point values.
o Cabs , cabs l finds absolute values for complex
numbers.
o labs finds absolute values for long double values.

•Declaration :-
•abs :-
Real - int abs (int x);
Complex - complex abs (complex z);
•Fabs , fabd l :-
double fabs (double x);
long double fabs (long double @E(x));
•Cabs , cabd l :-
double cabs (struct_complex z);
long double cabd l (struct_complexl z);
•Labs :-
long int labs(long int x);

 This header file contains prepackaged
functions to perform various operations on
‘characters’.
 To include this header file in the program use
the preprocessor directive-
# include < ctype.h >

 toupper is a function which converts lowercase
characters to uppercase characters. If the input
character is already uppercase character then
those characters remain unchanged.
 _toupper is a macro which also converts
lowercase characters to uppercase characters.
But if the input characters have uppercase
characters in it then the result of _toupper is
‘undefined’.

•Declarations :-
1. int toupper (char ch);
2. Int _toupper (char ch);

 tolower is a function which converts uppercase
characters to lowercase characters. If the input
character is already lowercase character then
those characters remain unchanged.
 _tolower is a macro which also converts
uppercase characters to lowercase characters.
But if the input characters have lowercase
characters in it then the result of _tolower is
‘undefined’.

•Declarations :-
1. int tolower (char ch);
2. Int _tolower (char ch);

 Isspace checks it out whether an input
character is a space , tab , carriage return , new
line , vertical tab , or formfeed or not.
 It is a macro and returns a non-zero value on
success.
 Declaration :-
int isspace ( int c );

 The lower order byte of character is in the
range 0 to 127.
 It is a macro and returns a non-zero value on
success.
 Declaration :-
int isascii (int c);

 Isprint checks it out whether the input
character is a printing character or not.
 It is also a macro and returns a non-zero value
on success.
 Declaration :-
int isprint (int c);

 Isgraph checks it out whether input character is
a printing character or not like isprint except
that space character is excluded.
 It is also a macro &returns non-zero value on
success.
 Declaration :-
int isgraph (int c);

 iscntrl checks it whether the input character is a
delete character or an ordinary control
character .
success.
 Declaration :-
int iscntrl ( int c);

 isxdigit checks out whether the input character
is a hexadecimal digit or not ( A to F , a to f , 0
to 9).
success.
 Declaration :-
int isxdigit (int c);

the preprocessor directive-
# include < stdlib.h >

 Abnormally terminates a process & writes a
termination message on stderr(“abnormal
program termination “) and then aborts the
program by a call to _exit with exit code 3.
 Declaration :-
void abort (void);

 atof converts a sting to floating point value .
 _atold converts a string to long double.
 Declaration :-
double atof (const char *s);
long double _atold (const char *(s));

 It is a macro that converts the string to integer.
 Declaration :-
int atoi (const char *s);

 Swab function copies nbytes from the “from”
string to the “to” string .nbytes should be even
.
 Adjacent even &odd bytes are swapped.
 This is useful for moving data from one
machine to another machine in different bytes
order.
 Declaration :-
void swab(char *from, char *to, int nbytes);

 System invokes the DOS command interpreter
file from inside an executing ‘c’ program to
execute a DOS command ,batch file , or other
program named by the string “command”.
 Declaration :-
int system (const char *command);

 time.h header file contains various functions
operating on time .
 Like clock, ctime, stime, time, difftime, acstime,
mktime, gmtime, localtime, etc.
preprocessor directive-
# include < time.h >

 Clock returns the number of clock ticks since
program start.
 Clock can be used to determine the time
interval between two events.
 Declaration :-
clock_t clock (void);

 Asctime converts date and time to ascii.
 Ctime converts date and time to a string.
 Declaration :-
char *acstime (const struct tm *tblock);
char *ctime (const time_t *time);

 mktime converts time to calendar format .
 Declaration :-
time_t mktime (struct tm *t);

 time gets time of day.
 stime gets system date and time.
 Declaration :-
time_t time (time_t *timer );
int stime (time_t *tp);

 Difftime computes difference between 2 times.
 Declaration :-
double difftime(time_t time2,time_t time1);

 Gmtime converts date and time to Greenwich
Mean Time (GMT).
 Localtime converts date and time to a structure.
 Declaration :-
struct tm *gmtime(const time_t *timer);
struct tm *localtime(const time_t *timer);

C standard library functions

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