UNIX Time or POSIX Time

#include <stdio.h>
#include <time.h>
int main()
{
	time_t sec;
	sec = time(NULL);

	printf("Number of hours since January 1, 1970 is %dId /n", sec/3600);
	return 0;
}

The following example shows the usage of rand() function.

#include 
#include 

int main()
{
	int i, n;
	time_t t;

	n = 5;

	/* Initializes random number generator */
	srand((unsigned) time(&t));

	/* Print 5 random numbers from 0 to 49 */
	for( i = 0; i < n; i++)
	{
		printf("%d\n", rand() % 50);
	}
	return(0);
}

The most important string functions are as follows:
strlen() Get length of a string.
strcat() Link together (concatenate) two strings.
strcmp() Compare two strings.
strchr() Find character in string.
strstr() Find string in string.
strlwr() Convert string to lowercase.
strupr() Convert string to uppercase.

#include <stdio.h>
#include <stdlib.h>

int main()
{
	char *t = "XXX";
	printf( "Length of <%s> is %d.\n", t, strlen( t ));
}