fgetc() reads the next character from stream and returns it as an unsigned char cast to an int, or EOF on end of file or error.
getc() is equivalent to fgetc() except that it may be implemented as a macro which evaluates stream more than once.
getchar() is equivalent to getc(stdin).
gets() reads a line from stdin into the buffer pointed to by s until either a terminating newline or EOF, which it replaces with '0'. No check for buffer overrun is performed (see BUGS below).
fgets() reads in at most one less than size characters from stream and stores them into the buffer pointed to by s. Reading stops after an EOF or a newline. If a newline is read, it is stored into the buffer. A '0' is stored after the last character in the buffer.
ungetc() pushes c back to stream, cast to unsigned char, where it is available for subsequent read operations. Pushed - back characters will be returned in reverse order; only one pushback is guaranteed.
fgetc(), getc() and getchar() return the character read as an unsigned char cast to an int or EOF on end of file or error.
gets() and fgets() return s on success, and NULL on error or when end of file occurs while no characters have been read.
Never use gets(). Because it is impossible to tell without knowing the data in advance how many characters gets() will read, and because gets() will continue to store characters past the end of the buffer, it is extremely dangerous to use. It has been used to break computer security. Use fgets() instead.