Tutorial 12
02. Display all prime numbers between two Intervals using a function.
#include <stdio.h>
int number(int);
int number (int n)
{
	int a,b,c=0;
	for (a=1; a<=n; a++)
	{
		if (n%a==0)
				c=c+1;	  
	}
	if (c<=2)
		printf("%i It is a prime number\n",n);
	else
		printf("%i It is not a prime number\n",n);
	return;
}
int main ()
{
	int x,y,n;
	printf("Enter Number");
	scanf("%i", &x);
	printf("Enter Number");
	scanf("%i", &y);
	for (x; x<=y; x++)
		number(x);	 
	return 0;
}
03. Find sum of natural numbers using a recursive function.
int sum_of_natural_numbers(int n) 
{
    if (n == 0) 
    {
        return 0;
    } 
    else 
    {
        return n + sum_of_natural_numbers(n - 1);
    }
}
int main() 
{
    int num;
	printf("Enter a positive integer: ");
	scanf("%d", &num); 
	if (num < 0) 
	{
		printf("Please enter a positive integer.\n");
		return 1;
    }
    printf("Sum of first %d natural numbers is: %d\n", num, sum_of_natural_numbers(num));
    return 0;
}
04. Calculate the power of a number using a recursive function.
#include <stdio.h>
double power(double base, int exponent) 
{
    if (exponent == 0) 
	{
        return 1;
    } 
	else if (exponent > 0) 
	{
        return base * power(base, exponent - 1);
    } else {
        return 1 / power(base, -exponent);
    }
}
int main() {
    double base;
    int exponent;
    printf("Enter the base: ");
    scanf("%lf", &base);
    printf("Enter the exponent: ");
    scanf("%d", &exponent);
    printf("Result: %.2lf\n", power(base, exponent));
    return 0;
}
05. Write a function to return the trip cost which calculated using the given distance in kilometers. Note: Take 35 LKR as travelling cost per kilometer.
#include <stdio.h>
    double calculate_trip_cost(double distance) {
    const double cost_per_km = 35.0;
    return distance * cost_per_km;
}
int main() {
    double distance;
    printf("Enter the distance in kilometers: ");
    scanf("%lf", &distance);
    printf("Trip cost: %.2lf LKR\n", calculate_trip_cost(distance));
    return 0;
}
06. Write a function to convert the LKR currency into US dollars.
#include <stdio.h>
double lkr_to_usd(double lkr_amount, double exchange_rate) 
{
    return lkr_amount / exchange_rate;
}
int main() 
{
    double lkr_amount, exchange_rate;
    printf("Enter the amount in LKR: ");
    scanf("%lf", &lkr_amount);
    printf("Enter the exchange rate (LKR to USD): ");
    scanf("%lf", &exchange_rate);
    printf("%.2lf LKR is equal to %.2lf USD\n", lkr_amount, lkr_to_usd(lkr_amount, exchange_rate));
    return 0;
}
