C/C++ programming functions

abs()	Int	Return absolute value	stdlib.h
acos()	Double	Return arc cosine	math.h
asin()	Double	Return arc sin	math.h
atan()	Double	Return arc tangent	math.h
atan2(d1,d2)	Double	Return arc tangent of d1/d2	math.h
atof()	Double	Convert string to double	stdlib.h
atoi()	Int	Convert string to integer	stdlib.h
atol()	Long	Convert string to long integer	stdlib.h
calloc(u1,u2)	Void	Return a pointer of the beginning allocate memory	malloc.h stdlib.h
ceil()	Double	Return round up value	math.h
cos()	Double	Return cosign	math.h
cosh()	Double	Return the hyperbolic cosine	math.h
difftime(l1,l2	Double	Return time difference l1-l2	time.h
exit()	Void	Close all file & buffer & terminate the program	stdlib.h
exp()	Double	Return the exponential value	math.h
fabs()	Double	Return the absolute value	math.h
fclose(f)	Int	Close file & return 0 if successful	stdio.h
feof()	Int	Determine if an end-of file condition has been reached. If so, return non zero else 0	stdio.h
fgetc(f)	Int	Enter a single character from file f	stdio.h
fgets(s,i,f)	Char	Enter string s, containing I characters, from file f	stdio.h
floor()	Double	Return round down value	math.h
fmod(d1,d2)	Double	Return remainder of d1%d2	math.h
fopen(s1,s2)	File	Open a file name s1 of type s2. Return a pointer to the file	stdio.h
fprintf(f,…)	Int	Send data item to file f, (remaining arguments are complicated)	stdio.h
fputc(c,f)	Int	Send a single character to file	stdio.h
fputs(s,f)	Int	Send a string to file	stdio.h
fread(s,i1,i2,f)	Int	Enter i2 data items, each of size i1 bytes, from file f to string s	stdio.h
free(p)	Void	Free a block of allocate memory whose beginning is indicated by p	malloc.h stdio.h
fscanf(f,…)	Int	Enter data item from the file f	stdio.h
fseek(f,l,i)	Int	Move the pointer for file f a distance l bytes from location i	stdio.h
ftell(f)	Long	Return the current pointer position within file f	stdio.h
fwrite(s,i1,i2,f)	Int	Enter i2 data items, each of size i1 bytes, from string s to file f	stdio.h
fetc(f)	Int	Enter a single character from file f	stdio.h
fetchar()	Int	Enter a single character from standard input device	stdio.h
gets()	Char	Enter a string  from keyboard	stdio.h
isalnum(c)	Int	Determine if argument is alphanumeric, return a non zero value if true else zero	ctype.h
isalpha(c)	Int	Determine if argument is alphabetic, return a non zero value if true else zero	ctype.h
isascii(c)	Int	Determine if argument is an ascii character, return a non zero value if true else zero	ctype.h
iscntrl(c)	Int	Determine if argument is ascii control character, return a non zero value if true else zero	ctype.h
isdigit(c)	Int	Determine if argument is a  decimal digit, return a non zero value if true else zero	ctype.h
isgraph(c)	Int	Determine if argument is a graphic ascii character, return a non zero value if true else zero	ctype.h
islower(c)	Int	Determine if argument is lowercase, return a non zero value if true else zero	ctype.h
issodigit(c)	Int	Determine if argument is an octal digit, return a non zero value if true else zero	ctype.h
isprint(c)	Int	Determine if argument is a printing ascii character, return a non zero value if true else zero	ctype.h
ispunct(c)	Int	Determine if argument is a punctuation character, return a non zero value if true else zero	ctype.h
isspace(c)	Int	Determine if argument is a white space character, return a non zero value if true else zero	ctype.h
isupper(c)	Int	Determine if argument is uppercase character, return a non zero value if true else zero	ctype.h
isxdigit(c)	Int	Determine if argument is a hexadecimal digit, return a non zero value if true else zero	ctype.h
labs(l)	Long	Return the absolute value	math.h
log(d)	Double	Return the natural logarithm	math.h
log10(d)	Double	Return the logarithm base 10 of d	math.h
malloc(u)	Void	Allocate u bytes of memory. Return a pointer to the beginning of the allocate space	malloc.h stdlib.h
pow(d1,d2)	Double	Return the d1 raise to the d2 power	math.h
printf(…)	Int	Send data item to the  standard output device	stdio.h
putc(c,f)	Int	Send  a single character to file f	stdio.h
putchar(c)	Int	Send a single character to the  standard output device	stdio.h
puts(s)	Int	Send a string  to the  standard output device	stdio.h
rand()	Int	Return a random positive integer	stdlib.h
rewind(f)	Void	Move the pointer to the beginning of the file f	stdio.h
scanf(…)	Int	Input data item to the  standard input device	stdio.h
sin(d)	Double	Return the sine of d	math.h
sinh(d)	Double	Return the hyperbolic sine of d	math.h
sqrt(d)	Double	Return the square root  of d	math.h
srand()	Void	Initialize the random number generator	stdlib.h
strstr(s1,s2) strcmp(s1,s2)	Int Int	Search string s2 from s1 Compare two string lexicographically. Return a negative value if s1<s2, positive if s1>s2, zero if s1==s2	string.h string.h
strcmpi(s1,s2)	Int	Compare two string lexicographically without regard to case. Return a negative value if s1<s2, positive if s1>s2, zero if s1==s2	string.h
strcpy(s1,s2)	Char	Copy string s2 to s1	string.h
strlen()	Int	Return the number of character in a string	string.h
strset(s,c)	Char	Set all character within s to c	string.h
strlwr(s)		Convert uppercase string to lowercase	string.h
strupr(s)		Convert lowercase string to uppercase	string.h
system(s)	Int	Pass command s to the operating system. Return 0 if the command is successfully executed else non-zero (-1)	stdlib.h
tan(d)	Double	Return the tangent value of d	math.h
tanh(d)	Double	Return the hyperbolic tangent value of d	math.h
time(p)	Long	Return the number of second elapsed beyond a designated base time	time.h
toascii(c)	Int	Convert value of argument to ascii	ctype.h
tolower(c)	Int	Convert upper to lowercase	ctype.h
toupper(c)	Int	Convert lowercase to upper	ctype.h

From: Me