68. Initialize Filter3 Class

Create a class Filter3 that represents a simple 3-coefficient digital filter used in embedded signal processing.

This problem focuses on correct use of constructor initialization lists in Embedded C++, which are mandatory when initializing const members and fixed-size arrays.

All internal members must be initialized using a constructor initialization list, not by assignment inside the constructor body.

Class Requirements

• Private Members
  • const int id
  • int coeff[3]
  • int lastOutput
• Constructor Requirements
  • Create the following constructor:

    • Filter3(int filterId, int c0, int c1, int c2)

  • The constructor must initialize all members using an initialization list:
    • id initialized with filterId
    • coeff initialized as {c0, c1, c2}
    • lastOutput initialized to 0
  • ❗ Assignment inside the constructor body is not allowed.
• Public Methods
  • void apply(int x)
    • Updates the output using the formula:

      • lastOutput = x * coeff[0] + coeff[1] + coeff[2]; 

  • int read()
    • Returns the current value of lastOutput

In main()

1. Read id, c0, c1, c2
2. Construct a Filter3 object
3. Read two input samples s1 and s2
4. Call apply(s1) and then apply(s2)
5. Print the final output using read()

Example Input

7 2 3 1
10 4

Example Output

12

Explanation

• Coefficients = {2, 3, 1}
• apply(10) → 10 * 2 + 3 + 1 = 24
• apply(4) → 4 * 2 + 3 + 1 = 12
• Final output = 12

Constraints

• Overflow handling is not required
• Input values remain within safe integer limits
• Output must match exactly