Convert ADC Reading to Battery Percentage

Level: Easy

Concepts: Variables & Data Types

Scenario

A handheld tester reads battery voltage via an ADC. You need to compute a percentage (0–100%) from the raw ADC count. The ADC’s full‑scale count can vary by hardware version.

Problem Statement

Write a function that converts a raw ADC reading to a battery‑percentage using integer arithmetic only.

Requirements

• Inputs: adc (current count), adc_max (maximum valid count).
• Use integer arithmetic; avoid floating point.
• Use overflow‑safe intermediate (long) for multiply.
• Perform round‑to‑nearest during percentage calculation.
• Clamp result to [0, 100].
• Treat invalid inputs as errors (adc_max <= 0 or adc < 0 or adc > adc_max).

Function Details

• Name: adc_to_percent
• Arguments:
  • int adc — Raw ADC count.
  • int adc_max — Maximum ADC count for the hardware (e.g., 1023, 4095).
  • int *out_percent — Output pointer for the result (0–100).
• Return Value: int — 0 on success; -1 on invalid inputs or null pointer.
• Description: Compute percent = round((adc * 100) / adc_max) using long for the product. Clamp to [0, 100]. Return an error if inputs are invalid or out_percent is NULL.

Solution Approach

(Use integer arithmetic with a long intermediate, add adc_max/2 for rounding, then clamp the result.)

Tasks to Perform

• Validate input arguments.
• Perform the integer calculation with proper rounding.
• Clamp the result to the range 0‑100.
• Store the result via out_percent.

Test Cases