Program

Char * getenv (const char * name) function searches the environment string pointed to by the name parameter and returns the value associated with that string.

The int system (const char * command) function passes the command name or program name specified by the command to the host environment to be executed by the Command processor and

Void function * bsearch (const void * key, const void * base, nitems, size, int (* compar) (const void *, const void *)) looks for an array of nitems objects, its original member

Void qsort function (void * base, so-phan-tu, kich-co, int (* compar) (const void *, const void *)) arranges an array.

The function int abs (int x) returns the absolute value of integer x.

Div_t div function (int numer, int denom) divides numer numerator for denom.

Function long int labs (long int x) returns the absolute value of x.

The div_t div function (long int numer, long int denom) divides the numerator numer to denom.

The function int rand (void) returns a random number in the range from 0 to RAND_MAX.

The function void srand (unsigned int seed) provides seed for the random number generator used by the rand function.

The function int mblen (const char * str, n) returns the length of a multi-byte char pointed to by parameter str.

Function size_t mbstowcs (* pwcs, const char * str, n) Converts the sequence of multi-byte char points pointed to by the parameter str to the array pointed to by pwcs.

Int mbtowc (wchar_t * pwc, const char * str, n) converts a range of bytes into a wide char.

The function int wctomb (char * str, wchar) converts the wide char into its multi-byte representation and stores it at the beginning of the character array pointed to by str.

The file header named string.h in C Library defines a variable type, a macro and various functions to manipulate character arrays.

The function void * memchr (const void * str, int c, size_t n) looks for the first occurrence of the character c (an unsigned char) in the first n bytes of the string pointed to by

The function int memcmp (const void * str1, const void * str2, size_t n)) compares the first n bytes of two strings str1 and str2.

Function size_t wcstombs (char * str, const wchar_t * pwcs, size_t n) convert wide-char string defined by pwcs into a multibyte string starting at str. Almost all n bytes are

Function void * memcpy (void * str1, const void * str2, size_t n) copies n characters from str2 to str1.

Char * function strstr (const char * haystack, const char * needle) looks for the final occurrence of the whole needle string (not including the ending null character) that is