1. Explain the algorithm ideas behind the push, pop, isFull, isEmpty functions? 
2. Explain the primary purpose of the following functions?

// Function 1
int IntStack::mysteryFunction1() const {
    int count = 0;
    for (int i = 0; i <= top; i++) {
        if (stackArray[i] % 2 == 0) {
            count++;
        }
    }
    return count;
}

// Function 2 
bool IntStack::mysteryFunction2() {
    if (isEmpty()) {
        return false;
    }
    for (int i = 0; i < top; i++) {
        stackArray[i] = stackArray[i + 1];
    }
    top--;
    return true;
}

// Function 3 
bool IntStack::mysteryFunction3(int k) {
    if (k < 1 || k > top + 1) {
        return false;
    }
    
    int targetIndex = top - k + 1;
    
    for (int i = targetIndex; i < top; i++) {
        stackArray[i] = stackArray[i + 1];
    }
    top--;
    return true;
}

3. Integrate these functions into the project and run a demo