Debugging Grimoire

weekday.c

Purpose

This C program demonstrates the use of enum, switch, and case constructs in C by working with days of the week. It includes functions to get the next and previous day and prints the corresponding day names.

Code Explanation

1. Enum Definition:

   • enum day {sun, mon, tue, wed, thu, fri, sat};
     Defines an enumerated type day to represent days of the week.

2. print_day Function:

   • Takes an enum day value as input and prints the corresponding day name using a switch statement. If the input is invalid, it prints an error message.

3. next_day Function:

   • Takes an enum day value as input and computes the next day based on modulo arithmetic.

4. previous_day Function:

   • Takes an enum day value as input and computes the previous day based on modulo arithmetic.

5. main Function:

   • Demonstrates how to use the enumerated type and the functions:
     • Initializes today as fri.
     • Prints the current day.
     • Prints an invalid day (to demonstrate error handling).
     • Prints the next and previous days.

Example Usage

Here’s how the program would behave:

enum day today = fri;
print_day(today);         // Outputs: friday
print_day(7);             // Outputs: 7 is an error
print_day(next_day(today)); // Outputs: saturday
print_day(previous_day(today)); // Expected Output: thursday

Output Example

When you compile and run the program:

friday
7 is an error
saturday
thursday

Complete Code

#include <stdio.h>

enum day {sun, mon, tue, wed, thu, fri, sat};

void print_day (enum day d) {
  switch(d) {
    case sun: printf("sunday"); break;
    case mon: printf("monday"); break;
    case tue: printf("tuesday"); break;
    case wed: printf("wednesday"); break;
    case thu: printf("thursday"); break;
    case fri: printf("friday"); break;
    case sat: printf("saturday"); break;
    default: printf("%d is an error", d);
  }
}

enum day next_day (enum day d) {
  return (d + 1) % 7;
}

enum day previous_day (enum day d) {
  return (d + 6) % 7;
}

int main() {
  enum day today = fri;
  print_day(today);
  printf("\n");
  print_day(7);
  printf("\n");
  print_day(next_day(today));
  printf("\n");
  print_day(previous_day(today));
  return 0;
}

Key Learning Points

• Enumerations (enum) are useful for defining named constants.
• switch and case statements simplify multi-branch conditional logic.
• Be cautious of operator precedence when performing arithmetic operations.