src: apply some fixes

[VoltrexKeyva]

• Use the %u format specifier for printing uint32_t.
• Cast the right-hand side of the condition of the for loop to uint8_t where it was implicitly promoted to int.
• Use int variable for getchar() since it can return EOF (-1) to indicate an error, char cannot hold negative integers.
• Use EOF instead of -1 to be idiomatic.