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

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

@@ -0,0 +1,16 @@
+#include "input.h"
+
+#include <stdio.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;
+}