C headers: in which header are input/output function prototypes and macros defined? Choose the correct standard header for stdio APIs.

Introduction / Context:
C provides standard I/O via a dedicated header that declares FILE, stream functions, macros, and related constants. This question targets recognition of the correct header file.

Given Data / Assumptions:

• We are referring to the ISO C standard library.
• Functions include printf, scanf, fopen, fclose, fgetc, fputc, etc.

Concept / Approach:

The header <stdio.h> declares standard input/output facilities: FILE, stdin, stdout, stderr, and functions like printf, scanf, fopen, fgets, and fwrite. Other headers serve different domains (stdlib.h for general utilities, string.h for strings, etc.).

Step-by-Step Solution:

Verification / Alternative check:

Any C reference will list <stdio.h> as the source of I/O declarations and macros like EOF and BUFSIZ.

Why Other Options Are Wrong:

conio.h: Non-standard, DOS/Windows compiler specific.

stdlib.h: General utilities (memory allocation, conversions, exit), not I/O streams.

dos.h: Non-standard DOS utilities.

Common Pitfalls:

• Confusing non-standard headers with ISO C headers.
• Assuming stdlib.h contains I/O because it is widely used.

Final Answer:

stdio.h