#include <stdio.h>

// given x calculate value of polynomial with coefficients a, b, c

double evaluate_quadratic(double a, double b,  double c, double x) {
    return (a * x * x) + (b * x) + c;
}

int main(int argc, char *argv[]) {
    double x;
    printf("Enter x: ");
    scanf("%lf", &x);

    double value = evaluate_quadratic(2.0, -3.0, 4.0, x);

    printf("2x^2 - 3x + 4 = %lf\n", value);

   return 0;
}

    #include <stdio.h>
#include <math.h>

// given x calculate value of polynomial with coefficients a, b, c

double quadratic_root(double a, double b,  double c) {
    return (-b + sqrt(b * b - 4 * a * c)) / (2 * a);
}

double evaluate_quadratic(double a, double b, double c, double x) {
    return (a * x * x) + (b * x) + c;
}

int main(int argc, char *argv[]) {
    double a, b, c;
    printf("Enter a: ");
    scanf("%lf", &a);
    printf("Enter b: ");
    scanf("%lf", &b);
    printf("Enter c: ");
    scanf("%lf", &c);

    double root = quadratic_root(a, b, c);

    printf("Calculated root is %lf\n", root);

    double value = evaluate_quadratic(a, b, c, root);

    printf("The value of the quadratic for  %lf is %lf\n", root, value);

    return 0;
}

    #include <stdio.h>

// calculate x to the power of 3
double cube(double x) {
    double result;
    result = x * x * x;
    return result;
}

int main(void) {
    double a, b;
    printf("42 cubed is %lf\n", cube(42.03));
    a = 2;
    b = cube(a);
    printf("2 cubed is %lf\n", b);
    return 0;
}

    #include <stdio.h>

void print_hundred_messages(void);
void print_ten_messages(void);
void print_message(void);

int main(int argc, char *argv[]) {
    print_hundred_messages();
    return 0;
}

void print_hundred_messages(void) {
    print_ten_messages();
    print_ten_messages();
    print_ten_messages();
    print_ten_messages();
    print_ten_messages();
    print_ten_messages();
    print_ten_messages();
    print_ten_messages();
}

void print_ten_messages(void) {
    print_message();
    print_message();
    print_message();
    print_message();
    print_message();
    print_message();
    print_message();
    print_message();
}

void print_message(void) {
    printf("C is good.\n");
    printf("C is great.\n");
    printf("We all love C.\n");
}

    #include <stdio.h>

int f(int x) {
    int y;
    // these assignments will have no effect on variables
    // outside the function
    x = x + 1;
    y = 3;
    return x * y;
}

int main(int argc, char *argv[]) {
    int  x, y , z;
    x = 1;
    y = 2;
    z = f(y);
    // note the variables x & y are local to main
    // and are not changed by assignment to variables
    // of the same name in f
    printf("x=%d y=%d z=%d\n", x, y, z);
    return 0;
}

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

int fibonacci(int n) {
     if (n < 2) {
        return 1;
     }
     return fibonacci(n - 1) + fibonacci(n-2);
}

int factorial(int n) {
     if (n < 2) {
        return 1;
     }
     return n * factorial(n - 1);
}

int main(void) {
    int x;

    printf("Enter number: ");
    scanf("%d", &x);

    printf("factorial %d = %d\n", x, factorial(x));
    printf("fibonacci %d = %d\n", x, fibonacci(x));

    return 0;
}