Structs (Answers)

Here is some additional practice using structs. Some of these might take a little bit of thinking, but this practice is here to help you get more comfortable with the material.

But first, some typedef fun.

typedef Practice

1. What should the blank lines be in line 9 to print out 100.00 - 89.00 = 11.00?

int main(void)
{
  typedef double more_precise_number;
  typedef float less_precise_number;

  more_precise_number x = 100;
  less_precise_number y = 89;

  printf("%___ - %___ = %___\n", x, y, x - y);

  return 0;
}

Answer: %lf, %f, and %lf since x is a double, y is a float, and their subtraction is also a double.

Onto Structs!

2. Given the following code, what would be printed in main()? Would it compile at all? Assume all necessary libraries are included.

struct my_structure
{
  int x;
  char text[64];
};

int main(void)
{
  struct my_structure structy_mc_struct_face;

  printf("%d\n", structy_mc_struct_face.x);

  return 0;
}

Answer: This is an undefined (garbage) value.

3. What about this? (Hint: An ASCII table is available here for your convience.)

struct my_structure
{
  int x;
  char text[64];
};

int main(void)
{
  struct my_structure structy_mc_struct_face;
  structy_mc_struct_face.x = 65;

  printf("%c\n", structy_mc_struct_face.x);

  return 0;
}

Answer: A

4. My hands are aching from writing code 24/7. I alone kept the 2018 electoral interference at bay. How can I save myself the 6 keystrokes and stop typing struct every time I want to create an instance of the my_structure struct? See the previous question on line 9 for reference.

Answer: After the struct declaration, add the following line:

typedef struct my_structure _______

This blank could be anything I desire, as long as I remember to use that for the rest of my code. This is a possible example:

struct my_structure
{
  int x;
  char text[64];
};

typedef struct my_structure my_s;

int main(void)
{
  my_s structy_mc_struct_face;
  structy_mc_struct_face.x = 65;

  printf("%c\n", structy_mc_struct_face.x);

  return 0;
}

Pointers of Structs

See the “Pointers Practice” page for practice on this!