Raindrops

Challenge Overview

Convert a number into its corresponding raindrop sounds - Pling, Plang and Plong.

Visit the raindrops exercise on Exercism to read the full instructions and download the exercise files.

Dig Deeper

if Statements

`if` Statements

raindrops.h

#ifndef RAINDROPS_H
#define RAINDROPS_H

void convert(char result[], int drops);

#endif

raindrops.c

#include "raindrops.h"

#include <stdio.h>
#include <string.h>

void convert(char result[], int drops)
{
   if (drops % 3 == 0)
      strcat(result, "Pling");
   if (drops % 5 == 0)
      strcat(result, "Plang");
   if (drops % 7 == 0)
      strcat(result, "Plong");

   if (strlen(result) == 0)
      sprintf(result, "%d", drops);
}

The first if statement checks if drops is a multiple of 3. If so, "Pling" is concatenated to result using the strcat function.
The second if statement checks if drops is a multiple of 5. If so, "Plang" is concatenated to result using the strcat function.
The thrd if statement checks if drops is a multiple of 7. If so, "Plong" is concatenated to result using the strcat function.

Finally, the [strlen function] checks if result is empty: if so, the [sprintf function] formats drops as string into result.

sprintf Function

`sprintf` Function

raindrops.h

#ifndef RAINDROPS_H
#define RAINDROPS_H

void convert(char result[], int drops);

#endif

raindrops.c

#include "raindrops.h"

#include <stdio.h>
#include <string.h>

void convert(char result[], int drops)
{
   sprintf(result, "%s%s%s", drops % 3 == 0 ? "Pling" : "",
           drops % 5 == 0 ? "Plang" : "", drops % 7 == 0 ? "Plong" : "");

   if (strlen(result) == 0)
      sprintf(result, "%d", drops);
}

This approach allows for very concise, if not a bit obfuscated, code.

A series of ternary conditional operators check if drops is a multiple of 3, 5, or 7 respectively. If it is, the expression returns the appropriate raindrop sound (either "Pling", "Plang" or "Plong"); otherwise, the result is the empty string ("").

Then, in the same statement, a single call to the sprintf function concatenates all the above three strings.

Finally, the strlen function checks if result is empty: if so, sprintf is used again to format drops as string into result.

Data-Driven Programming

raindrops.h

#ifndef RAINDROPS_H
#define RAINDROPS_H

void convert(char result[], int drops);

#endif

raindrops.c

#include "raindrops.h"

#include <stdio.h>
#include <string.h>

typedef struct {
   int factor;
   const char *sound;
} sound_t;

static const sound_t SOUNDS[] = {
   { 3, "Pling" },
   { 5, "Plang" },
   { 7, "Plong" },
};

#define ARRAY_SIZE(arr) (sizeof(arr) / sizeof(arr[0]))

void convert(char result[], int drops)
{
   for (size_t i = 0; i < ARRAY_SIZE(SOUNDS); i++) {
      if (drops % SOUNDS[i].factor == 0) {
         strcat(result, SOUNDS[i].sound);
      }
   }

   if (strlen(result) == 0) {
      sprintf(result, "%d", drops);
   }
}

First, the program defines a structure data type to hold together two pieces of information: a factor and its corresponding sound. Then, an array is created to hold all the necessary data, which is used to drive the logc of the program.

The body of the function does not have any knowledge of the actual data, becoming simple and flexible:

For each element of the SOUNDS array — If the given number is a multiple of the current factor --- Then concatenate the current sound to the result string using the strcat function.

This approach allows for extensible code: for example, new sounds could be added (or removed) without modifying the convert function.

Finally, the [strlen function] checks if result is empty: if so, the [sprintf function] formats drops as string into result.

Source: Exercism c/raindrops