input: Write a function named `generate_first_n_primes` that takes an integer `n` as input and returns a list of the first `n` prime numbers. If `n` is less than or equal to 0, return an empty list.
  assert generate_first_n_primes(5)==[2, 3, 5, 7, 11]
  assert generate_first_n_primes(1)==[2]
  assert generate_first_n_primes(0)==[]
  assert generate_first_n_primes(10)==[2, 3, 5, 7, 11, 13, 17, 19, 23, 29]
  assert generate_first_n_primes(-1)==[]
output: def generate_first_n_primes(n):
      if n <= 0:
          return []
      primes = []
      num = 2
      while len(primes) < n:
          is_prime = True
          for prime in primes:
              if num % prime == 0:
                  is_prime = False
                  break
          if is_prime:
              primes.append(num)
          num += 1
      return primes