wrong input will exit the program c++ - c++

Question

So I have started to learn c++ and I have wrote this simple program , when a user inputs wrong number it gives an option to try again however when a user inputs any characters it gives the option to try again and directly exits the program why is that happening ?
`
#include<unistd.h>
#include<stdio.h>
int main(){
int a;
char b ,c;
start:
printf("INPUT ONLY NUMBER 1 : ");
scanf(" %d", &a);
if(a==1)
{
printf( " you entered correctly \n");
printf("do you want to try again? <Y> <N> \n");
scanf(" %c", &c);
if(c=='Y' ||c=='y')
{
goto start;
}
}
else {
sleep (1);
printf("wrong number , do you want to try again? <Y> <N> \n");
scanf(" %c" , &b);
}
if (b=='Y'||b=='y')
{
sleep(1);
goto start;
}
else
if(b=='n'||b=='N')
{
sleep(1);
printf("thank you and goodbye");
exit (1);
}
}
`

Answer 1

scanf(" %d")
I bet your problem comes from that space before the %d. Try scanf("%d"). Same later: scanf("%c") instead of scanf(" %c ").
Anyway, your code is VERY dirty. And this looks like C, not C++.
Not trying to be a maniac here, but you should indent properly and AVOID the goto BY ALL MEANS. Your program structure is simple and a while loop will do the trick for you. You should also avoid to explicitly call exit(1). exit is mostly used to provoke premature termination. In your case, your program reaches its end normally, and you should exit with your main function's return 0.
#include <unistd.h>
#include <stdio.h>
#include <stdbool.h> //Reauired to use boolean type in C
int main()
{
bool stop = false; //boolean type only has two states: true and false. Very useful for loops!
while(!stop) //Read as "While we don't need to stop, execute the loop's contents
{ //Much easier to read!
printf("INPUT ONLY NUMBER 1 : ");
scanf("%d", &a);
if(a == 1)
{
printf("you entered correctly \n");
printf("do you want to try again? <Y> <N>\n");
scanf("%c", &c);
if(c == 'N' || c == 'n')
{ //We only need to tell the loop when to stop
stop = true; //by setting stop to true
} //The loop's default behavior is to loop execution of its content
}
else
{
sleep(1);
printf("wrong number , do you want to try again? <Y> <N> \n");
scanf("%c" , &b);
if(b=='n'|| b=='N')
{
stop = true; //Same as above
}
sleep(1);
}
}
printf("thank you and goodbye");
return 0;
}

Answer 2

There is something left behind from your scanf, which sometimes you can clean that up flushing it, but in your code seems not to work.
Having a look at that issue this comes across:
http://c-faq.com/stdio/stdinflush2.html
Which basically tells you that if your approach does not work, then you should change it.
Hope this help, you also asked about while in one of your questions there, so:
#include <iostream>
int main(){
char input;
char try_again;
do {
std::cout << "INPUT ONLY NUMBER:";
std::cin >> input;
// http://en.cppreference.com/w/cpp/string/byte/isdigit
// does not return a bool, you can check that >0
if (std::isdigit(input)) {
// do what you want.
std::cout << "digit\n";
continue;
} else {
// you can as for more imput like:
std::cout << "Not a number, try again?(y/Y):";
std::cin >> try_again;
std::tolower(try_again);
if (try_again == 'y') {
continue; // will start the loop again.
} else {
break; // it will exit the loop.
}
}
} while(true);
return 0;
}