1

🔫

Towers Open Fire

Cooldown timers plus your nearestInRange from Part 1

Active

🎯

Goal for this step

Make towers spawn bullets at the nearest target on a cooldown.

1Continue in your Part 1 project, every system plugs in.
2Bullet struct: position, target enemy index/pointer, speed 340, damage copied from the tower.
3Each tower: cooldown −= dt; at ≤ 0 with a target from nearestInRange → push a bullet, reset cooldown to 0.7 s.
4Draw bullets as small yellow circles.

tower.cpp

struct Bullet {
    sf::Vector2f pos;
    Enemy* target;
    float speed = 340;
    int damage;
};

std::vector<Bullet> bullets;

for (auto& t : towers) {
    t.cooldown -= dt;
    if (t.cooldown <= 0) {
        Enemy* target = nearestInRange(t, enemies);
        if (target) {
            bullets.push_back({ t.pos, target, 340, t.damage });
            t.cooldown = 0.7f;
        }
    }
}

✏️

Fill in the Blanks

+15 XP

A tower may fire when its reaches zero AND nearestInRange returns a target instead of . Firing resets the cooldown to 0.7 s.

🧠

Knowledge Check

+15 XP

Why does the cooldown only reset when a shot is actually fired?

ATo save memory

BSo a tower with no targets fires the INSTANT one appears, rather than being mid-cooldown for nothing

CCooldowns cannot reset twice

2

🎯

Homing Bullets

Chase the target using Part 1 vector maths

Locked

🎯

Goal for this step

Bullets home in, hit, damage, and clean themselves up.

1Bullet update = enemy path-following aimed at a moving point: normalise (target − pos), move by speed·dt.
2Within 8 px: apply damage, mark the bullet dead. Dead or escaped target? Kill the bullet too (its pointer is stale!).
3Enemy hp ≤ 0 → alive = false and pay the bounty: gold += e.bounty;
4Clean dead bullets with erase-remove (Episode 3-4 skill). Fire away!

tower.cpp

for (auto& b : bullets) {
    if (!b.target->alive) { b.dead = true; continue; }
    sf::Vector2f d = b.target->pos - b.pos;
    float len = std::sqrt(d.x*d.x + d.y*d.y);
    if (len < 8.f) {
        b.target->hp -= b.damage;
        if (b.target->hp <= 0) {
            b.target->alive = false;
            gold += b.target->bounty;
        }
        b.dead = true;
    } else {
        b.pos += (d / len) * b.speed * dt;
    }
}
bullets.erase(std::remove_if(bullets.begin(), bullets.end(),
    [](const Bullet& b){ return b.dead; }), bullets.end());

⌨️

Code Challenge

+20 XP

Pay the bounty on a kill:

tower.cpp

b.target->hp -= b.;
if (b.target->hp <= ) {
    b.target->alive = false;
    gold += b.target->;
}

💡 Hint: The bullet carries its damage; death is zero-or-less hp; the kill reward was staged in Part 1.

🧠

Knowledge Check

+15 XP

Why must a bullet die when its target dies?

ABullets are expensive

BIts target pointer now refers to a dead enemy, chasing it is meaningless and using it after removal is dangerous

CSFML limits bullets

3

🌊

The Wave System

Timed spawning of escalating enemy groups

Locked

🎯

Goal for this step

Spawn enemies in numbered waves with growing difficulty.

1Wave state: number, enemies left to spawn, a spawn-gap timer (0.8 s), and a between-waves rest (5 s).
2Wave n: 4 + n*2 enemies, hp 20 + n*8, speed 70 + n*4.
3All spawned AND all dead/escaped → rest timer → next wave.
4HUD: "Wave 3, 6 enemies remain" and "Next wave in 3…" during rests. Information is a tower defence player’s oxygen.

tower.cpp

int wave = 0, toSpawn = 0;
float spawnGap = 0, rest = 3;

if (toSpawn == 0 && enemiesCleared(enemies)) {
    rest -= dt;
    if (rest <= 0) {
        wave++;
        toSpawn = 4 + wave * 2;
        rest = 5;
    }
} else if (toSpawn > 0) {
    spawnGap -= dt;
    if (spawnGap <= 0) {
        Enemy e;
        e.pos = path[0];
        e.hp = 20 + wave * 8;
        e.speed = 70 + wave * 4;
        enemies.push_back(e);
        toSpawn--;
        spawnGap = 0.8f;
    }
}

✏️

Fill in the Blanks

+15 XP

Wave n spawns 4 + n× enemies with a second gap between them, followed by a second rest before the next wave.

🧠

Knowledge Check

+15 XP

The rest period between waves exists so players can…

AGet snacks

BSpend their bounty gold, build and upgrade between assaults. Tension, release, decision. That is the TD loop

CLet the CPU cool down

4

⬆️

Tower Upgrades

Right-click to upgrade: damage, range, fire rate

Locked

🎯

Goal for this step

Add a 3-level upgrade path that changes the maths meaningfully.

1Tower gains int level = 1. Right-clicking one (mouse within 20 px of its centre) upgrades if gold allows.
2Cost 40×level. Effects per level: damage +4, range +25, cooldown ×0.8.
3Show level as small pips on the tower; deepen its colour per level.
4Strategy emerges: three level-1 towers or one level-3? (Spoiler: focused fire usually wins, let players discover it.)

tower.cpp

// on right-click near tower t:
int cost = 40 * t.level;
if (gold >= cost && t.level < 3) {
    gold -= cost;
    t.level++;
    t.damage += 4;
    t.range  += 25;
    t.fireTime *= 0.8f;    // faster firing
}

⌨️

Code Challenge

+20 XP

Apply the level-up bonuses:

tower.cpp

t.level++;
t.damage += ;
t.range  += ;
t.fireTime *= f;

💡 Hint: Damage grows by four, range by twenty-five, and the time between shots shrinks to 80%.

🧠

Knowledge Check

+15 XP

Multiplying fireTime by 0.8 per level (instead of subtracting) means…

AUpgrades get weaker

BCompounding: 0.7s → 0.56s → 0.45s, each level stays a meaningful % boost without ever hitting zero

CThe tower jams

5

🐉

The Boss Wave

Wave 10: a tank with a health bar leads the charge

Locked

🎯

Goal for this step

Cap the game with a boss that tests the player’s whole build.

1Wave 10 spawns one BOSS: hp 600, speed 40, bounty 200, drawn twice the size with a floating health bar.
2A boss health bar: red back-bar + green front scaled by hp/maxHp, hovering above it (you have built this bar in two languages!).
3Boss escapes → instant defeat (lives = 0). Boss dies → VICTORY screen.
4A slow tank rewards sustained damage, upgraded tower clusters shine, exactly what the player has been learning to build.

tower.cpp

if (wave == 10 && toSpawn == 1) {     // last spawn = the boss
    Enemy boss;
    boss.pos = path[0];
    boss.hp = 600;  boss.maxHp = 600;
    boss.speed = 40;
    boss.bounty = 200;
    boss.isBoss = true;
    enemies.push_back(boss);
    toSpawn = 0;
}

// boss escape = instant loss:
if (e.isBoss && e.wp >= (int)path.size())
    lives = 0;

✏️

Fill in the Blanks

+15 XP

The boss has hp but only speed 40, a slow . If it escapes, lives drops instantly to .

🧠

Knowledge Check

+15 XP

A good final boss tests…

AReaction speed only

BEverything the game taught: economy, placement, upgrades, a slow tank is an exam on total damage output

CThe pause button

6

🏆

Victory, Defeat & Series Wrap

End screens, restart, and your C++ journey reviewed

Locked

🎯

Goal for this step

Finish the game and take stock of a serious achievement.

1DEFEAT at lives ≤ 0; VICTORY when the boss dies. Both freeze play, show wave reached + towers built, R restarts fresh.
2What you used across 7 episodes: compilation & linking, dt physics, structs/classes/enums, deque/vector, pointers & nullptr, normalised vectors, erase-remove, cooldown systems, state machines.
3That list IS an engine-programming foundation. Unreal C++ will read like your own code.
4Series complete. Take the quiz, claim the badge, and go build something nobody has seen before. ⚙️🎉

💡

Want to keep going in C++? Add tower types (slow/splash), a second map, or save the best wave to a file. Every one is within your reach now.

✏️

Fill in the Blanks

+15 XP

Across the series you used std::deque for , normalised vectors for following, and nullptr-returning searches for tower .

🧠

Knowledge Check

+15 XP

The single most C++-specific superpower you practised in this series is…

ADrawing rectangles

BChoosing precise tools, structs vs classes, deque vs vector, pointers, enums, control over exactly how data lives

CUsing the mouse

Wave After Wave!Tower Defence Part 2

Wave After Wave!
Tower Defence Part 2