The function getenv () in Cchar * getenv (const char * name) function searches the environment string pointed to by the name parameter and returns the value associated with that string.
System () function in Cthe 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 returned after the command is completed.
The function bsearch () in Cvoid 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 is point to by base, for a member that connects the object pointed to by the key. the size of each array element is
Function abs () in Cthe function int abs (int x) returns the absolute value of integer x.
Div () function in Cdiv_t div function (int numer, int denom) divides numer numerator for denom.
Labs () function in Cfunction long int labs (long int x) returns the absolute value of x.
The function rand () in Cthe function int rand (void) returns a random number in the range from 0 to rand_max.
Calloc () function in Cthe function void * calloc (so-phan-tu, kich-co-phan-tu) allocates the requested memory and returns a pointer to it. the difference between malloc and calloc is: malloc does not set memory to 0 while calloc sets the allocated memory to 0.
Free () function in Cthe void free function (void * ptr) frees the previously allocated memory by a call to calloc, malloc, or realloc
Malloc () function in Cthe malloc () function allocates the requested memory and returns a pointer to it.
Function realloc () in Cthe realloc () function attempts to recover the memory block pointed to by the ptr pointer that was previously allocated with a call to malloc or calloc.
The function getenv () in C
char * getenv (const char * name) function searches the environment string pointed to by the name parameter and returns the value associated with that string.
