| void abort(void); | Prints "Abnormal program termination" and raises SIGABRT. |
| void system(const char *s); | Passes command string s to command processor for execution. |
| int abs(int); | Returns absolute value of an integer. |
| long labs(long x); | Returns absolute value of a long integer. |
| int atexit(void (*func)(void)); | Allows you to define a function to be executed when the exit function is called. |
| void exit(int status); | Exits program with status code for OS. |
| double atof(const char *s); | Converts an ascii string to a floating point number. |
| int atoi(const char *s); | Converts an ascii string to an integer number. |
| long atol(const char *s); | Converts and ascii string to a long integer number. |
| div_t div(int numer, int denom); | Do integer division getting quotient and remainder |
| ldiv_t ldiv(long numer, long denom); | Do long integer division getting quotient and remainder |
| void *malloc(size_t size); | Dynamically allocate storage of size bytes. |
| void *calloc(size_t n, size_t size); | Dynamically allocate storage for n items of size bytes each. |
| void *realloc(void *block, size_t size); | |
| Allows you to reallocate storage that was previously allocated. | |
| void free(void *block); | Releases dynamically allocated memory so it can be reused. |
| int rand(void); | Computes a series of pseudo-random numbers. |
| void srand(unsigned seed); | Uses seed as a seed for a new sequence of pseudo-random numbers to be returned by subsequent calls to rand(). |
| double strtod(const char *s, char **endptr); | |
| Converts string to double value. | |
| long strtol(const char *s, char **endptr, int radix); | |
| unsigned long strtoul(const char *s, char **endptr, int radix); | |
| Converts initial portion of string s to unsigned long or long. endptr points to where conversion terminated. radix is the numeric base of the number represented by the string. | |
| char *getenv(const char *name); | Gets the environment variable value by name. |
| void qsort(void *base, size_t nelem, size_t width, int (*fcmp)(const void *, const void *)); | |
| Sorts an array in memory. fcmp is a user defined function that is used to compare two data items in the array. It must return -1, 0 or 1 depending on whether the first arg is less than, equal to or greater than the second arg. | |
| void *bsearch(const void *,const void *,size_t,size_t,int (*fcmp)(const void *, const void *)); | |
| Performs a binary search on an array in memory. The second arg points to an item you wish to search for. fcmp is same as qsort(). | |