if
(
(
output
=
fopen
(
outputfilename
,
"r+"
)
)
!=
NULL
)
{
printf
(
"Output file already exists. Overwrite? (y/n)"
)
;
scanf
(
" %c"
,
&
answer
)
;
if
(
answer
==
'n'
)
{
return
0
;
}
}