The header file <stdlib.h> defines a number of types, macros, and functions of general utility.

Types
div_t Structure containing quotient and remainder after division of ints
ldiv_t Structure containing quotient and remainder after division of longs
lldiv_t Structure containing quotient and remainder after division of long longs
String to number conversions
atoi Convert string to int
atol Convert string to long
atoll Convert string to long long
strtol Convert string to long
strtoll Convert string to long long
strtoul Convert string to unsigned long
strtoull Convert string to unsigned long long
Number to string conversions
itoa Convert int to string
ltoa Convert long to string
lltoa Convert long long to string
utoa Convert unsigned to string
ultoa Convert unsigned long to string
ulltoa Convert unsigned long long to string
Integer arithmetic functions
div Divide two ints returning quotient and remainder
ldiv Divide two longs returning quotient and remainder
lldiv Divide two long longs returning quotient and remainder
Pseudo-random sequence generation functions
RAND_MAX Maximum value returned by rand
rand Return next random number in sequence
srand Set seed of random number sequence