string.h
	strlen()    : Computes the length of a cstring
    	strcpy()    : Copies one cstring into another cstring
    	strncpy()   : Copies n characters from one cstring into another cstring
    	strcat()    : Concatenates one cstring with another
    	strncat()   : Concatenates n characters from one cstring with another cstring
    	strcmp()    : Compares two cstrings 
    	strncmp()   : Compares n characters in two cstrings
    	strchr()    : Computes the position of a character in a string
    	strspn()    : Computes the length of the portion of a cstring that is composed of the characters from a second cstring
    	strcspn()   : Computes the length of the portion of a cstring that is not composed of any character from a second cstring
    	strdup()    : Allocates necessary memory and duplicates a cstring into newly allocated memory
    	strtok()    : Breaks a cstring into tokens based on given delimiter characters in another cstring
    	strsep()    : Breaks a cstring into tokens like strtok().
    	memset()    : Sets the value of all characters in a cstring
    	memcpy()    : Copies the bytes from one area of memory into another non-overlapping area of memory
    	memmove()   : Copies the bytes from one area of memory into another area of memory (two areas can overlap with each other)

stdlib.h
	exit()	    : Terminates a process
    	malloc()    : Allocates memory dynamically
    	calloc()    : Allocates memory dynamically
    	free()      : Releases dynamically allocated memory
    	atoi()      : Converts a cstring into an integer
    	strtol()    : Converts a cstring into a long integer
    	strtoul()   : Converts a cstring into an unsigned long integer
    	strtoll()   : Converts a cstring into a long long integer
    	strtof()    : Converts a cstring int a float
    	strtod()    : Converts a cstring into a double.
	srandom()   : Sets the seeds of random number generator.
	random()    : Generates a random number.

stdio.h
    	printf()    : Prints a formatted output onto the screen
    	sprintf()   : Prints a formatted output into a cstring buffer.
   	fopen()	    : Opens a file stream to read or write. Returns a FILE pointer.
    	fclose()    : Closes an open file stream.
    	fprintf()   : Prints a formatted output into a file stream specified by a FILE pointer.
   	fgets()	    : Gets cstring from a file stream.
    	fread()	    : Reads a block of bytes from a file stream.
    	fwrite()    : Writes a block of bytes into a file stream.
    	fseek()	    : Sets the read or write position of an open file stream.
    	fflush()    : Flushes write file stream data from memory onto the disk. Depending on the implementation, it also clears read file stream memory. 
    	getline()   : Gets an entire line delimited with a new line character from a file stream specified by a FILE pointer.
	getdelim()  : Gets an entire line delimited by given delimiter character from a file stream specified by a FILE pointer.
 	dprintf()   : Prints a formatted output into a file or a socket stream specified by a file descriptor