Expression must have a constant value. the value of variable " NUM_DOCS" "NUM_PATS" cannot be used as a constant

Question

void GenerateClinic()
   {
    int NUM_DOCS = (rand() % 100) + 1; //cannot be used as a 
   constant
   const int NUM_PATS = (rand() % 500) + 1; //cannot be used as a 
   constant

    Doctor testDoc[NUM_DOCS]; //error is NUM_DOCS
    
    Patient testPat[NUM_PATS]; //error is NUM_PATS

    
    for (int i = 0; i < NUM_DOCS; i++)
    {
        int room = i;

        int code = (rand() % 12) + 1; //random specialty code

        //Doctor name becomes "doctor (index + 1)"
        string number = to_string(i + 1);
        string name = "doctor ";
        name.append(number);

        //sets doctor and assigns appropriately
        testDoc[i].setName(name);
        testDoc[i].setRoom(room);
        testDoc[i].setCode(code);

        assignGenerated(testDoc[i]);
    }