How to check whether the user input is a number in C

bool isNumber(char number[])
{
    int i = 0;

    // Check if it is a negative number
    if (number[0] == '-')
        i = 1;
    for (; number[i] != 0; i++)
    {
        if (!isdigit(number[i]))
		//if (number[i] > '9' || number[i] < '0')
            return false;
    }
    return true;
}