How to Fix Error: 'for' loop initial declarations are only allowed in C99 mode

Understand the Error

• This error typically occurs when you declare variables in the initialization part of a `for` loop, which is allowed in C++, and since C99 for C. In pre-C99 versions of the C standard, variable declarations must be at the start of a block, not within a `for` statement.
• As a firmware developer using C++, this error might indicate incorrect file interpretation as C code rather than C++. Ensure that your files are being compiled as C++.

Ensure Correct Compilation Mode

• Verify that your build system or compiler command is set to compile sources as C++. For GCC, use the `g++` compiler instead of `gcc` to ensure that files are processed as C++.
• Check the Makefile or build scripts for flags like `-std=c++11` or `-std=gnu++11` to indicate C++ compile mode. For example:

  ```bash
  g++ -std=c++11 -o output_file source_file.cpp
  ```

Inspect Your Code

• Examine your loop declarations and ensure they conform to C++ standards. For instance, the following loop is valid in C++ and C99:

  ```cpp
  for (int i = 0; i < 10; ++i) {
  // Your code here
  }
  ```

• Ensure no inadvertent use of C89 conventions in portions of your code intended to be C++. Review any project files and transform them if needed, according to C++ syntax rules.

Update Your Compiler

• If problems persist despite correct settings, consider updating your compiler. Modern compilers better distinguish between C and C++ and support newer language standards.
• Using a current version ensures access to compatibility features and bug fixes from previous releases, thus minimizing chances of encountering mode-related compilation issues.

Check for External Libraries or Scripts

• Ensure any scripts, libraries, or preprocessor directives correctly specify the intended language version. They should not force C compilation on C++ code.
• Adapt any imported C-based libraries to conform to C++ if necessary or maintain separation within the project to prevent cross-mode compilation errors.

Consider IDE and Tools Configuration

• Sometimes, integrated development environments (IDEs) or associated tools misconfigure projects. Double-check settings to confirm that they do not override file-type propagation or compile-time mode selection.
• Ensure that your IDE is set up for C++ development, possibly contributing to better context-sensitive help and error detection.