Constexpr ADC Temperature Table

Question

Problem: Constexpr ADC Temperature Table. Solve this hands-on electronics task on EWskills.

Accepted Answer

#include 
using namespace std;

// Compile-time temperature lookup table
constexpr int TEMP_TABLE[6] = { -40, -10, 20, 50, 80, 120 };

int main() {
    int idx;
    cin >> idx;

    cout << TEMP_TABLE[idx];

    return 0;
}

Explanation & Logic Summary

TEMP_TABLE is declared as constexpr, so it is evaluated entirely at compile time
The table is stored in Flash / ROM, not RAM
Runtime execution performs a constant-time (O(1)) lookup
No arithmetic or floating-point computation occurs at runtime
This guarantees deterministic execution time

Firmware Relevance & Real Embedded Meaning

In memory-constrained embedded systems (8 KB–32 KB MCUs):

constexpr tables save RAM by residing in Flash
Lookup tables eliminate costly runtime math
Immutable data prevents accidental modification
Compilers can aggressively optimize constant access

This pattern is commonly used in:

Thermistor temperature conversion
Battery voltage-to-percentage mapping
Display gamma correction
Motor control profiles
Sensor calibration data

Using a non-constexpr array would:

Consume RAM
Require runtime initialization
Allow unintended modification
Reduce optimization opportunities

For these reasons, constexpr lookup tables are standard practice in production embedded firmware.

64. Constexpr ADC Temperature Table