1th: Compile cleanly at high warning level

A high degree of caution, using the compiler's highest warning level, requires a neat construction (no warning), an understanding of all warnings, and elimination by modifying the code rather than by lowering the warning level. The way to exclude a warning is to get it clear first, then rewrite the code to exclude the warning and make the code reader and compiler clearer.

A successful build should be silent, even if it starts to work properly, but it may hide the danger of future real warnings.

For example, warning signed and unsigned mismatches (signed/unsigned mismatch), there is usually no need to compare and assign different integers to the symbol, and the type of operation should be changed to make the type match.

1th: Compile cleanly at high warning level