feat(solutions): add is-palindrome/c/function

challenges/is-palindrome/solutions/c/function/string.c

@@ -0,0 +1,47 @@
+#include "string.h"
+
+#include <stdbool.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "character.h"
+
+char* string_to_upper(const 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_upper(string[index]));
+  }
+  return result;
+}
+
+char* string_reverse(const char* string) {
+  size_t string_length = strlen(string);
+  char* result = malloc(sizeof(char) * (string_length + 1));
+  for (size_t index = string_length - 1; index != -1; index--) {
+    character_append(result, string[index]);
+  }
+  return result;
+}
+
+bool string_is_palindrome(const char* string) {
+  char* string_reversed = string_reverse(string);
+  bool is_palindrome = strcmp(string_reversed, string) == 0;
+  free(string_reversed);
+  return is_palindrome;
+}
+
+char* string_replace(const char* string, char search_value,
+                     char replace_value) {
+  size_t string_length = strlen(string);
+  char* result = malloc(sizeof(char) * (string_length + 1));
+  for (size_t index = 0; index < string_length; index++) {
+    bool is_search_value = search_value == string[index];
+    if (is_search_value) {
+      character_append(result, replace_value);
+    } else {
+      character_append(result, string[index]);
+    }
+  }
+  return result;
+}