#include <stdio.h>// used by all 3
#include <math.h>   // Used by square root only function used from it is pow() in square root
//and doesn't really need to be here
#include <stdlib.h> // used by Random numbers
#include <time.h>   // used by time

int main() {
	menu();
}

int menu() {
	int select;
	double num;
	char flag;
	printf("1: Square Root\n");
	printf("2: Random Numbers\n");
	printf("3: Display Time/Date\n");
	printf("4: Quit\n");
	printf("What function would you like to use?: ");
	scanf("%d", &select);
	switch (select) {
		case 1:
			printf("Enter a number greater than 0: ");
			scanf("%lf", &num);
			sqroot(num);
			break;
		case 2:
			randn();
			break;
		case 3:
			distime();
			break;
//any additional menu entries can be placed here and their numbers changed accordingly
//conforming to the format already specified here.
		case 4:
			return(0);
		default:
			printf("Invalid Selection. Try again?(y/n): ");
			scanf("%c", &flag);
			if (flag == 'y')	
				menu();
			else
				return(0);
//Test here to keep from infinitely looping when an input of the wrong type is used
//on the menu.
	}
}

int sqroot(double num) {
	double lastNum = 0;
	double errorMargin = 0.000001, test = 1;
//errorMargin: The precision to which the approximation of the square root
//is to be held to
	int i = 0;
	while (num <= 0) {
		printf("Please enter a number greater than 0.\n");
		printf("Enter: ");
		scanf("%lf", &num);
	}
	lastNum = num;
	while ((test * 2) < num) {
		test += test;
//using the 2^n closest to the test number as the initial guess for Newton's method
	}
	while ((lastNum-test) > errorMargin) {
		lastNum = test;
		test = (test - ((pow(test, 2) - num)/(2 * test)));
//Apply Newton's method until the difference between the previous approximation
//and the current one is less than or equal to the errorMargin
	}
	printf("The square root of %f is: %f\n", num, test);
	menu();
}

int randn() {
	int num;
	srand(time(NULL)); //Seed rand() with the current epoch time
//better seeding strategies can be used here to make the number more random.
	num = rand();      
//Should be a perfectly random number so long as it is not run twice in the same second.
	printf("Your random number is: %d\n", num);
	menu();
//To make this number random between 1 and some max value for say a dice roller,
//use the modulus operator (%) on the num variable for the max number you want and 
//then add 1 to the number to make it 1-max rather than 0-(max-1)
}

int distime() {
	time_t now;
	time(&now);
	printf("%s", ctime(&now));
//give ctime the struct filled by time(&now) to output the time and date 
//in a nicely formatted string
	menu();
}

//Place the definitions of any additional functions here.
//should include their name, return type and all other things needed
//to run them.