Challenge: Define a Counter Account (PDA)

Add a Counter account struct and update the Initialize accounts to create it as a Program Derived Address (PDA).

What is a PDA?

A PDA is an account address derived deterministically from seeds and the program ID. Unlike keypair accounts, PDAs don't have a private key — the program itself controls them. The same seeds always produce the same address.

For our counter: seeds = ["counter", user_wallet_pubkey] means each wallet gets exactly one counter per program.

Requirements

1. Add a Counter struct with #[account] attribute containing pub count: u64 and pub authority: Pubkey
2. Add lifetime <'info> to the Initialize struct
3. Add a counter field with #[account(init, payer = user, space = 8 + 8 + 32, seeds = [b"counter", user.key().as_ref()], bump)]
4. Add a user field as Signer<'info> with #[account(mut)]
5. Add system_program as Program<'info, System>

What Each Constraint Does

• init — creates the account (allocates space, assigns owner)
• payer = user — the user account pays the rent deposit
• space = 8 + 8 + 32 — 8 bytes discriminator + 8 bytes u64 + 32 bytes Pubkey
• seeds — the byte arrays used to derive the PDA address
• bump — Anchor finds the valid bump seed automatically
• mut on user — required because their lamport balance changes (pays rent)

Tips

• The Counter struct goes outside the #[program] module
• The Initialize struct needs a lifetime parameter: pub struct Initialize<'info>
• Make sure counter has type Account<'info, Counter>
• The authority field records who created the counter (useful for access control later)