Random Numbers

Generates and displays random 16-bit numbers on button press. Every game needs randomness — enemy spawns, item drops, damage variance, shuffle order. The SNES has no hardware RNG, so we use a software pseudo-random number generator (LFSR) seeded from the frame counter.

Screenshot

What You'll Learn

• How to generate random numbers with rand() (returns 0-65535)
• How to seed the PRNG with srand() for unpredictable sequences
• Why seeding from getFrameCount() at a player-triggered moment gives good randomness
• How to display numbers in both hex and decimal with the text module

Controls

Button	Action
A	Generate a new random number
B	Re-seed the PRNG from the frame counter

SNES Concepts

Why Seed Matters

rand() produces a deterministic sequence — the same seed always gives the same numbers. For a game, you want unpredictability. The trick: call srand(getFrameCount()) when the player presses START on the title screen. Since the player presses at an unpredictable frame, the seed varies each playthrough.

Using rand() in Games

u16 enemy_x = rand() % 256;        // Random X position (0-255)
u16 damage = 10 + (rand() % 6);    // Damage 10-15
u8 drop = (rand() % 100) < 20;     // 20% chance of item drop

Modules Used

Module	Why it's here
console	consoleInit(), WaitForVBlank(), NMI handler setup
sprite	OAM buffer (required by NMI handler)
dma	DMA transfers used internally by console init
background	BG layer configuration
text	textInit(), textPrintAt(), textFlush() for number display
input	padPressed() for single-press button detection

Build & Run

cd $OPENSNES_HOME
make -C examples/basics/random

Open random.sfc in Mesen2. Press A repeatedly, then press B and press A again — the sequence changes.