You could fairly easily create your own portable stdint.h equivalent in C89 (using the preprocessor and INT_MAX etc.). I remember doing that in the 90s, before

You could fairly easily create your own portable stdint.h equivalent in C89 (using the preprocessor and INT_MAX etc.). I remember doing that in the 90s, before C99. However, it was also conventional wisdom to use int by default to match the architecture’s “natural” word size, and maybe add a preprocessor check when you needed it to be 32-bit. Another consideration is that the built-in types have to be used with the C standard library functions to some extent.