# Data Types and Fixed-width Integers — Arduino & Embedded C

Source: https://www.geekswithgeeks.com/en/arduino-embedded-c/fixed-types

> Why uint8_t beats int on a microcontroller.

## Sizes that depend on the target

In C and C++ the size of `int` depends on the platform. On 8-bit AVR boards such as the Uno R3, `int` is **16 bits** (range -32768 to 32767) and `double` is the same 32-bit type as `float`; on 32-bit boards like the ESP32, `int` is 32 bits. Code that silently overflows on one board can work on another. `<stdint.h>` provides **fixed-width types**: `uint8_t`, `int16_t`, `uint32_t` and so on, which say exactly what you mean and save precious RAM. Watch for overflow in intermediate expressions (for example `1000 * 100` overflows a 16-bit int) and prefer integer maths over floating point on chips without a hardware FPU.

## Below the Arduino API

Embedded C gives you exact sizes, memory placement and direct control of hardware registers.

![Three ideas: fixed-width types, memory types, registers and volatile.](assets/figures/arduino-embedded-c/section-6-map.svg) — Figure 6.1 — Types, memories and registers inside the MCU.

## Overflow on a 16-bit int

Plain embedded C; behaviour noted for AVR (16-bit int).

```c
#include <stdint.h>

uint8_t  brightness = 255;   /* 0..255, one byte */
int16_t  offset     = -40;   /* signed, two bytes */
uint32_t uptime_ms  = 0;     /* large counter, four bytes */

void example(void) {
    int16_t bad = 1000 * 100;           /* overflow: 100000 does not fit in 16 bits */
    int32_t good = 1000L * 100;         /* L suffix forces 32-bit arithmetic */
    uint32_t scaled = (uint32_t)brightness * 1000u / 255u;  /* widen before multiplying */
    (void)bad; (void)good; (void)scaled;
}
```

## Use the smallest correct type

Pick the smallest type that can hold the full range, but widen before multiplying. Saving a byte is pointless if the arithmetic overflows.

**Quiz:** How many bits is an int on an ATmega328P-based Arduino Uno R3?

- [ ] 32
- [ ] 8
- [x] 16
- [ ] 64

*Answer:* 16. AVR-GCC uses a 16-bit int, unlike most 32-bit platforms.