Array Practice (Solutions)

1. Write a line of code that declares an array called uv_levels that contains 5 integers.

Answer:

int uv_levels[5];

2. Which element of the array does the following expression refer to?

numbers[3]

Answer: The fourth element of the array.

3. What is the difference between the 4 in each of the following statements?

int numbers[4];

numbers[4] = 25;

Answer: In the first statement, the 4 indicates an array size, in this case creating an array of four elements. In the second statement, the 4 indicates a particular element, in this case the fifth element of the numbers array. (Bonus: This second statement would actually be considered improper in the context of the first statement, as there are only four elements, where the fifth element is attempted to be accessed.)

4. What will be the output of the following program? If there is an error in the code, explain what the error is instead.

#include <stdio.h>

void increase_by_one(int array[], int length)
{
  for (int i = 0; i < length; i++)
  {
    array[i]++;
  }
}

int main(void)
{
  int array[5] = {1, 2, 3, 4, 5};

  increase_by_one(array, 5);

  for (int i = 0; i < 5; i++)
  {
    printf("%d\n", array[i]);
  }

  return 0;
}

Answer:

Output of the program is as follows:

2
3
4
5
6

5. Fill in the blanks to initialize an array with 10 doubles, starting at 0 and incrementing by 0.5 for each value. In other words, the final array should contain [0.0, 0.5, 1.0, 1.5, 2.0, ..., 4.5].

Answer:

#include <stdio.h>

void initialize(double *array, int length)
{
  for (int i = 0; i < length; i++)
  {
    array[i] = 0.5 * i;
  }
}

int main(void)
{
  // Create the array
  double array[10];

  // Initialize array values
  initialize(array, 10);

  // View the values in the array
  for (int i = 0; i < 10; i++)
  {
    printf("array[%d] = %0.1lf\n", i, array[i]);
  }

  return 0;
}

6. Fill in the blanks for the program to create an array of odd numbers from 1 to max, which will be inputted by the user.

Answer:

int main(void)
{
  int max;
  printf("Enter the maximum number to go to: ");
  scanf("%d", &max);

  int size = (max + 1) / 2;
  int odd = 1;
  int odd_numbers[size];

  for (int i = 0; i < size; i++)
  {
    odd_numbers[i] = odd;
    odd = odd + 2;
  }

  for (int i = 0; i < size; i++)
  {
    printf("%d\n", odd_numbers[i]);
  }

  return 0;
}

7. Fill in the blanks for the program to initialize the final array with the squares of the numbers of the initial array. That is, if initial is array of with elements [1, 2, 3, 4, 5], our program will initialize the corresponding final array with the values squared as [1, 4, 9, 16, 25]. Make sure you accept arrays of any size!

Answer:

double square(double num)
{
  return num * num;
}

void init_square_array(double *initial, double *final, int count)
{
  for (int i = 0; i < count; i++)
  {
    final[i] = square(initial[i]);
  }
}

void print_array(double *array, int count)
{
  printf("These are the values of the array!\n");
  for (int i = 0; i < count; i++)
  {
    printf("%lf\n", array[i]);
  }
}

int main(void)
{
  double numbers[] = { 1, 2, 3, 4, 5 };
  double numbers_results[5];

  double evens[10];
  double evens_results[10];

  double x = 2;
  for (int i = 0; i < 10; i++)
  {
    evens[i] = x;
    x = x + 2;
  }

  init_square_array(numbers, numbers_results, 5);
  init_square_array(evens, evens_results, 10);

  print_array(numbers_results, 5);
  print_array(evens_results, 10);

  return 0;
}

8. Create a function that takes two integer arrays, array1 and array2, and the length of array1, that copies the contents of array1 into array2. Assume that array2 has at least as many elements as array1.

Answer:

void copy_array(int *array1, int *array2, int length)
{
  for (int i = 0; i < length; i++)
  {
    array2[i] = array1[i];
  }
}

9. What is wrong with the following code snippet? (Challenge yourself to avoid using your code editor.)

#include <stdio.h>

void print_float_array(float *array, int count)
{
  for (int i = 0; i < count; i++)
  {
    printf(" %f", array[i]);
  }
  printf("\n");
}

int main(void)
{
  float values[] = {3.14, 2.718, 6.9, 42.0};

  for (int i = 0; i < 4; i++)
  {
    print_float_array(values[i], 4);
  }

  return 0;
}

Answer: print_float_array() accepts a float array and a count, but line 18 is passing a float value, not an array. Also, since we iterate the for loop 4 times in main(), in which we call a function that goes throes another loop 4 times, we would be doing twice the amount of work. To fix it, we would simplify the code in main() to:

int main(void)
{
  float values[] = {3.14, 2.718, 6.9, 42.0};

  print_float_array(values, 4);

  return 0;
}

10. Create a function that adds 5 to every odd element of an array of integers. Assume you are provided an integer array (called array) and an integer representing the number of elements in the array (called length).

    Answer: First, we must figure out what the function declaration will look like. If we are given an integer array and the number of elements, the parameters may look like (int *array, int length) or (int array[], int length).

    Next, we must figure out the return type of the function. Since we are modifying the array in-place, this function does not need to return anything. This makes the return type void.

    Finally, we will call the function add_five_to_odd. With this, we can get the function declaration:

    void add_five_to_odd(int *array, int length)
    {
      // Your code here
    }

    This function should traverse through the array, and if it finds an odd element (using the modulus operation), five should be added to this element. In total, this function may look like the following:

    void add_five_to_odd(int *array, int length)
    {
      for (int i = 0; i < length; i++)
      {
        if (array[i] % 2 == 1)
        {
          array[i] += 5;
        }
      }
    }