错误：从“ int”转换为“ uint8_t”可能会更改其值[-Werror = conversion]

Question

我在<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script> <img src="https://example.com/img_01.png" /> <img src="https://example.com/img_02.png" /> <img src="https://example.com/img_03.png" /> <img src="https://example.com/img_04.png" />上编译了以下代码，这给了我如下错误：

GCC compiler

我不明白这里的问题。

error: conversion to 'uint8_t' from 'int' may alter its value [-Werror=conversion]

第1行出现问题并给出错误。