03_bf.c

static void jumpFront(const char *str, int *index) {
  if (str[*index] != '[')
    return;
  for (int count = 0; str[*index] != '\0'; (*index)++) {
    if (str[*index] == '[')
      count++;
    else if (str[*index] == ']')
      count--;
    if (count == 0)
      break;
  }
}

static void jumpBack(const char *str, int *index) {
  if (str[*index] != ']')
    return;
  for (int count = 0; *index >= 0; (*index)--) {
    if (str[*index] == '[')
      count--;
    else if (str[*index] == ']')
      count++;
    if (count == 0)
      break;
  }
}

static int brainfuck(const char *str) {
  static int data[100];

  int pointer = sizeof(data) / sizeof(int) / 2;
  for (int index = 0; str[index] != '\0'; index++) {
    switch (str[index]) {
    case '+':
      data[pointer]++;
      break;
    case '-':
      data[pointer]--;
      break;
    case '>':
      pointer++;
      break;
    case '<':
      pointer--;
      break;
    case '.':
      // No device to output to...
      break;
    case ',':
      // No device to input from...
      break;
    case '[':
      if (data[pointer] == 0)
        jumpFront(str, &index);
      break;
    case ']':
      if (data[pointer] != 0)
        jumpBack(str, &index);
      break;
    }
  }
  return data[pointer];
}

int main(int argc, char **argv) {
  // Run argv[1] as brainf*ck code.
  return brainfuck(argv[1]);
}