Question

This does not work. It gives an error regarding ISO C++ forbidding initialization.

class hash_map 
{
private:
    hash_entry **table;
    const int TABLE_SIZE = 128;
public:
    hash_map() 
    {
        table = new hash_entry*[TABLE_SIZE];
        for (int i = 0; i < TABLE_SIZE; i++)
            table[i] = NULL;
    }
    int get(int key) 
    {
        int hash = (key % TABLE_SIZE);
        while (table[hash] != NULL && table[hash]->getKey() != key)
            hash = (hash + 1) % TABLE_SIZE;
        if (table[hash] == NULL)
            return -1;
        else
            return table[hash]->getValue();
    }
    void put(int key, int value) 
    {
        int hash = (key % TABLE_SIZE);
        while (table[hash] != NULL && table[hash]->getKey() != key)
            hash = (hash + 1) % TABLE_SIZE;
        if (table[hash] != NULL)
            delete table[hash];
        table[hash] = new hash_entry(key, value);
    }
    ~hash_map() 
    {
        for (int i = 0; i < TABLE_SIZE; i++)
            if (table[i] != NULL) delete table[i];
        delete[] table;
    }
};

Answer 1

const int TABLE_SIZE = 128;

This is the cause of the compilation error. It is allowed in C++11 only, not in C++03 and C++98.

Either make it a static member of the class, OR initialize it in the constructor. Make use of member-initialization-list for it.

Apart from that dont forget to implement copy-semantics following Rule of Three, OR disable it altogether by declaring them (don’t define them) in the private section. I think, disabling it would make more sense in this case.