char array read

    c++ (maybe c) question time
    i need to make a string class. i'm not allowed to use the c++ one.
    so what i don't get is how the fuck i read a string and save it into a array. i mean, i just don't see how. i've been looking around but i don't find anything that fits what i need
    all i need is that. reading a string and saving it into an array. if someone can guide me i'd be thankful.

    also it has to be dynamic, so no char arr[1000000000000000]

It would be better to store the characters in a relational database instead.