feat(solutions): add slugify/c/function

challenges/slugify/solutions/c/function/README.md

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+# slugify/c/function
+
+Created by [@Divlo](https://github.com/Divlo) on 10 November 2021.

challenges/slugify/solutions/c/function/character.c

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+#include "character.h"
+
+#include <stdbool.h>
+#include <stdlib.h>
+#include <string.h>
+
+void character_append(char* string, char character) {
+  size_t length = strlen(string);
+  string[length] = character;
+  string[length + 1] = '\0';
+}
+
+char character_to_lower(char character) {
+  char ascii_a = 'a';
+  char ascii_A = 'A';
+  char ascii_Z = 'Z';
+  if (character >= ascii_A && character <= ascii_Z) {
+    return character + (ascii_a - ascii_A);
+  }
+  return character;
+}
+
+bool character_is_alphanumeric(char character) {
+  char ascii_a = 'a';
+  char ascii_A = 'A';
+  char ascii_z = 'z';
+  char ascii_Z = 'Z';
+  char ascii_0 = '0';
+  char ascii_9 = '9';
+  return (character >= ascii_a && character <= ascii_z) ||
+         (character >= ascii_A && character <= ascii_Z) ||
+         (character >= ascii_0 && character <= ascii_9);
+}

challenges/slugify/solutions/c/function/character.h

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+#ifndef __CHARACTER__
+#define __CHARACTER__
+
+#include <stdbool.h>
+
+/**
+ * @brief Append a character to a string, assuming string points to an array
+ * with enough space.
+ *
+ * @param string
+ * @param character
+ */
+void character_append(char* string, char character);
+
+/**
+ * @brief Converts the character to lowercase.
+ *
+ * @param character
+ * @return char
+ */
+char character_to_lower(char character);
+
+/**
+ * @brief Checks if the character is alphanumeric.
+ *
+ * @param character
+ * @return bool
+ */
+bool character_is_alphanumeric(char character);
+
+#endif

challenges/slugify/solutions/c/function/input.c

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+#include "input.h"
+
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "character.h"
+
+char* input() {
+  char character;
+  size_t length = 1;
+  char* string = malloc(length * sizeof(char));
+  *string = '\0';
+  while ((character = getchar()) != '\n' && character != EOF) {
+    length++;
+    string = realloc(string, length * sizeof(char));
+    character_append(string, character);
+  }
+  return string;
+}

challenges/slugify/solutions/c/function/input.h

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+#ifndef __INPUT__
+#define __INPUT__
+
+/**
+ * @brief Read a line from stdin.
+ *
+ * @return char*
+ */
+char* input();
+
+#endif

challenges/slugify/solutions/c/function/solution.c

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+#include <stdio.h>
+#include <stdlib.h>
+
+#include "character.h"
+#include "input.h"
+#include "string.h"
+
+int main() {
+  char* string = input();
+  string = string_trim(string, ' ');
+  string = string_trim(string, '-');
+  string = string_to_lowercase(string);
+  string = string_slugify(string);
+  printf("%s\n", string);
+  free(string);
+  return EXIT_SUCCESS;
+}

challenges/slugify/solutions/c/function/string.c

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+#include "string.h"
+
+#include <stdbool.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "character.h"
+
+char* string_trim_start(char* string, char character) {
+  size_t string_length = strlen(string);
+  char* result = malloc(sizeof(char) * (string_length + 1));
+  size_t index_space = 0;
+  while (string[index_space] == character) {
+    index_space++;
+  }
+  for (size_t index = index_space; index < string_length; index++) {
+    character_append(result, string[index]);
+  }
+  return result;
+}
+
+char* string_trim_end(char* string, char character) {
+  size_t string_length = strlen(string);
+  char* result = malloc(sizeof(char) * (string_length + 1));
+  size_t index_space = string_length - 1;
+  while (string[index_space] == character) {
+    index_space--;
+  }
+  for (size_t index = 0; index < index_space + 1; index++) {
+    character_append(result, string[index]);
+  }
+  return result;
+}
+
+char* string_trim(char* string, char character) {
+  char* result = string_trim_start(string, character);
+  result = string_trim_end(result, character);
+  return result;
+}
+
+char* string_to_lowercase(char* string) {
+  size_t string_length = strlen(string);
+  char* result = malloc(sizeof(char) * (string_length + 1));
+  for (size_t index = 0; index < string_length; index++) {
+    character_append(result, character_to_lower(string[index]));
+  }
+  return result;
+}
+
+char* string_slugify(char* string) {
+  size_t string_length = strlen(string);
+  char* result = malloc(sizeof(char) * (string_length + 1));
+  int words = 0;
+  char* current = malloc(sizeof(char) * (string_length + 1));
+  for (size_t index = 0; index < string_length; index++) {
+    if (string[index] == ' ' || (string[index] == '-' && strlen(current) > 0)) {
+      strcat(result, current);
+      character_append(result, '-');
+      memset(current, 0, sizeof(char) * (string_length + 1));
+      words++;
+    } else {
+      if (character_is_alphanumeric(string[index])) {
+        character_append(current, string[index]);
+      }
+    }
+  }
+  strcat(result, current);
+  free(current);
+  return result;
+}

challenges/slugify/solutions/c/function/string.h

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+#ifndef __STRING__
+#define __STRING__
+
+/**
+ * @brief Removes all `character` from the start of a string.
+ *
+ * @param string
+ * @return char*
+ */
+char* string_trim_start(char* string, char character);
+
+/**
+ * @brief Removes all `character` from the end of a string.
+ *
+ * @param string
+ * @return char*
+ */
+char* string_trim_end(char* string, char character);
+
+/**
+ * @brief Removes all `character` from the start and end of a string.
+ *
+ * @param string
+ * @return char*
+ */
+char* string_trim(char* string, char character);
+
+/**
+ * @brief Converts all the alphabetic characters in a string to lowercase.
+ *
+ * @param string
+ * @return char*
+ */
+char* string_to_lowercase(char* string);
+
+/**
+ * @brief Generate a slug from a string.
+ *
+ * @param string
+ * @return char*
+ */
+char* string_slugify(char* string);
+
+#endif