Stdio.h

Formatted input output functions
printf(): Prints formatted output.
fprintf(): Prints formatted output to a file.

scanf():Reads formatted input.
fscanf()
sscanf()

Unformatted input output functions
getc(): Reads a character.
getchar()
gets(): Reads array of characters.
fgets():
puts():Writes array of characters.
putchar():
putc(): writes a character.
fgetc(): Reads a character from file.
fputc(): Writes a character into a file.
fputs()
getw()
putw()
fgetchar()
fputchar()
fgetchar
fgetc()

File access functions
fopen(): Opens  file.
fclose(): Closes file.
fflush(): Synchronizes an output stream with the actual file.
fseek():Moves the file position indicator to a specific location in a file.
ftell():
rewind():Moves the file position indicator to the beginning in a file.
remove(): Erases a file.

Error handling functions
clearerr():Clears errors.
feof():Checks for the end-of-file.

Reference:
https://en.m.wikipedia.org/wiki/C_file_input/output#/search