给出正整数 num,返回 true 如果 num 是完整的正方形或假的. 完整的正方形是整数的正方形. 换句话说,它是某个整数与自身的乘法. 你不能使用任何内置的库函数,如 sqrt.
Here's the solution in Python:

```
def isPerfectSquare(num):
    i = 1
    while (i*i <= num):
        if (i*i == num):
            return True
        i += 1
    return False
```

The function takes in a positive integer `num` and checks if it is a perfect square by iterating through all numbers `i` starting from 1 and checking if `i*i` equals `num`. If `i*i` exceeds `num`, then `num` is not a perfect square and the function returns False.