update C snipplets

code/C/Strings/buffer_len.h

@@ -0,0 +1,4 @@
+/* size_t strlen(const char *s); */
+
+size_t length;
+length = strlen("Example string");

code/C/Strings/clear_string.c

@@ -0,0 +1,9 @@
+int main(int argc, char const *argv[]) {
+  char *buffer = malloc(256 + 1);
+
+  buffer[0] = '\0';
+  strcpy(buffer, "");
+  memset(buffer, '\0', sizeof(buffer));
+
+  return 0;
+}