C Program Won't Print Line, Already tried flush - c

Question

The program is supposed to get user first name and last name and then print them as last name, first name. The program stops immediately after the second input. I tried fflush (stdout) but that didn't seem to work (I might have done it incorrectly).
#include "stdafx.h"
#include <iostream>
using namespace System;
using namespace std;
int main()
{
char First[30], Last[30];
printf("Please type in your First Name: ");
scanf("%s",&First);
fflush(stdout);
printf("Please type in your Last Name: ");
scanf("%s",&Last);
printf("%s %s", Last, First);
printf("pause");
return 0;
}

Answer 1

C++ version of your program :
#include <iostream>
using namespace std;
int main()
{
string first, last;
cerr << "Please type in your First Name: ";
if (! (cin >> firs))
return -1;
cerr << "Please type in your Last Name: ";
if (! (cin >> last))
return -1;
cout << last << ' ' << first << endl;
return 0;
}
Compilation and execution :
pi#raspberrypi:/tmp $ g++ -pedantic -Wextra i.cc
pi#raspberrypi:/tmp $ ./a.out
Please type in your First Name: aze
Please type in your Last Name: qsd
qsd aze
pi#raspberrypi:/tmp $
I check names was enter (no EOF), I use cerr to be sure to flush the messages without writing endl
And the C version :
#include <stdio.h>
int main()
{
char first[30], last[30];
fprintf(stderr, "Please type in your First Name: ");
if (scanf("%29s", first) != 1)
return -1;
fprintf(stderr, "Please type in your Last Name: ");
if (scanf("%29s", last) != 1)
return -1;
printf("%s %s\n", last, first);
return 0;
}
Compilation and execution:
pi#raspberrypi:/tmp $ gcc -pedantic -Wextra i.c
pi#raspberrypi:/tmp $ ./a.out
Please type in your First Name: aze
Please type in your Last Name: qsd
qsd aze
I limit the size in the scanf to not write out of the arrays, I check scanf was able to read the names, I also use stderr to be sure to flush the message without writing '\n'
first and last are array, it is useless to use '&' in the scanf to give their address
Note these versions do not allow to enter composed names using spaces, to allow that all the line need to be read

Answer 2

It helps to think about the purpose of the fflush() call. There is pending data that you want the user to see so they know what to type.
Let us consider the first query (printf, scanf, flush). The printf() puts data into a buffer. The scanf() then reads the user's response. The flush() won't execute until after the user has typed something.
Those three calls are in the wrong order. I'll leave fixing that as an exercise for the reader.
Now consider the next query (printf, scanf). The printf() puts data into a buffer. The scanf() reads the user's response, but the user won't yet have seen the "... Last Name:" prompt.
Clearly there is also an error in that block. Again, I'll leave fixing that as an exercise for the reader. Hint: if you fixed the first error that should help you understand the second.
By the way, scanf() doesn't guard against overflowing the First[] and Last[] arrays. That isn't necessary to answer your original question, but I mention it because even after you have fixed the code it will remain unsafe.

Answer 3

The fflush(stdout); you have doesn't help because it's too early in the code as it doesn't help with flushing the latter printfs.
You could use \n to flush as well. But this may not work if your output device isn't interactive e.g. redirected to a file.
You also have another problem with scanf() format specifiers: First and Last, being arrays, decay into pointers when passed to scanf. So you are passing the wrong type of arguments to scanf - just drop the &'s from scanf calls.
So your program could simply be:
#include <stdio.h>
int main(void)
{
char First[30], Last[30];
printf("Please type in your First Name: ");
scanf("%s", First);
fflush(stdout);
printf("Please type in your Last Name: ");
scanf("%s", Last);
fflush(stdout);
printf("%s %s\n", Last, First);
fflush(stdout);
getchar();
return 0;
}
All the fflush(stdout) calls may not be necessary if you could use \n in all printf calls because you're likely using an interactive terminal.
If you are using C++, you should really be using iostream for I/O. If nothing else, scanf is a terrible, has many problems, and should be avoided.