Functions

By: Jerrett Longworth, Idel Martinez

Variable Scope

This is one of the most important topics in programming, especially in the C language. This starts by looking at variable scope without functions, then bringing them into the mix later.

Will this code compile? Explain why or why not. If it does compile, what will be printed?

#include <stdio.h>

int main(void)
{
  int my_number = 5;
  printf("The value of my_number is: %d\n", my_number);

  {
    int my_number = 10;
  }

  printf("The value of my_number is: %d\n", my_number);

  return 0;
}

Variable Scope with Functions

This is important to get right. Functions are the base of every program, and knowing what your variables are doing in them is crucial.

Fill in the blank so that all the types match correctly. By the way… What do lines 10 and 15 print?

_____ add_everything(_____ num1, int num2)
{
  return num1 + num2;
}

int main(void)
{
  int x, y;

  printf("%_____\n", add_everything(10, 5));

  x = 20;
  y = 15;

  printf("%d\n", add_everything(x, y));

  return 0;
}

What happens when you return a value from a function? Things can get tricky if you’re snoozing… What’s the value of floaty_float after the execution of this program, assuming the user enters 5?

void get_value(float f)
{
  scanf("%f", &f);
  f = f + 0.5;
}

int main(void)
{
  float floaty_float;
  get_value(floaty_float);

  printf("%f\n", floaty_float);

  return 0;
}

What if the previous example is altered a little? What happens to floaty_float? Assume, again, that the user enters 5.

float get_value(void)
{
  float f;
  scanf("%f", &f);
  return f + 15.5;
}

int main(void)
{
  float floaty_float;
  floaty_float = get_value();

  printf("%f\n", floaty_float);

  return 0;
}

What will main print in lines 10, 12, and 14?

void add_num(int x, int y)
{
  x = x + y;
}

int main(void)
{
  int x = 10;

  printf("At first x was %d\n", x);
  add_num(20, 10);
  printf("Now x is %d\n", x);
  add_num(x, 10);
  printf("While x is now %d\n", x);

  return 0;
}

What will main print in lines 12, 14, and 16?

int x;

void add_num(int y)
{
  x = x + y;
}

int main(void)
{
  x = 10;

  printf("At first x was %d\n", x);
  add_num(20);
  printf("Now x is %d\n", x);
  add_num(10);
  printf("While x is now %d\n", x);

  return 0;
}

Creating Functions

Define a function that calculates the slope between the two points using the fancy function header:

// Return the slope of two points.
double slope(float x1, float y1, float x2, float y2)
{
  // This is the function body. Your code goes here.
}

int main(void)
{
  double point_x1 = 10;
  double point_x2 = 40.55;
  double point_y1 = 98.122321;
  double point_y2 = 12;

  printf("The first point is: (%lf.2, %lf.2)\n" point_x1, point_y1);
  printf("The second point is: (%lf.2, %lf.2)\n", point_x2, point_y2);
  printf("The slope of the points is %lf\n", slope(point_x1, point_y1, point_x2, point_y2));

  return 0;
}

CHALLENGE: Define a function that accomplishes the following task using the function header: (Hint: You may use the sqrt() function provided by the math.h library.)

// Return the distance between two points.
double distance_between_points(float x1, float y1, float x2, float y2)
{
  // Code goes here.
}

int main(void)
{
  double p_x1, p_x2, p_y1, p_y2;

  printf("Please enter the first point\n");
  printf("> x: ");
  scanf("%lf", &p_x1);
  printf("> y: ");
  scanf("%lf", &p_y1);

  printf("Please enter the second point\n");
  printf("> x: ");
  scanf("%lf", &p_x2);
  printf("> y: ");
  scanf("%lf", &p_y2);

  printf("The distance between these two points is %lf\n", distance_between_points(p_x1, p_y1, p_x2, p_y2));

  return 0;
}

Functions with Loops

CHALLENGE BONUS: Write a mario() function that prints an m x n block using # characters.

// Example output:

// mario(3, 4) should print:
// ###
// ###
// ###
// ###

// mario(1, 1) should print:
// #

// mario(10, 5) should print:
// ##########
// ##########
// ##########
// ##########
// ##########

void mario(int m, int n)
{
  // Your code here
}

int main(void)
{
  int m, n;

  printf("Enter a width: ");
  scanf("%d", &m);
  printf("Enter a height: ");
  scanf("%d", &n);

  mario(m, n);

  return 0;
}

Fun fact: This problem is based on the one seen in CS50.