C++ Being able to exit from a function at any given time - c++

Question

This example is a very basic and simple program.
I want to be able to exit from a function whenever the user wants to.
In the add() function i'm able to exit on the
cin>>NumA;
line by typing 9999 and it will return me to the menu. However i would only be able to exit at this point, so if i wanted to exit at any time i'd have to add the
if (NumA == 9999)
{
return;
}
throught all of the program. I want to be able to exit at any time inside of the function, even better if it can be done by pressing a key, like backspace.
I suppose there is a better way to implement this, how can i do this? Maybe another function :^)
void add()
{
cout << "Addition" << endl;
cout << "Number A: ";
int NumA;
cin>>NumA;
if (NumA == 9999)
{
return;
}
cout << "Number B: ";
int NumB;
cin>>NumB;
int Result = NumA + NumB;
cout << NumA << " + " << NumB << " = " << Result<<endl;
}
int main()
{
int Op;
do
{
cout << "Main" << endl;
cout << "1) Add" << endl;
cout << "2) Another function call" << endl;
cout << "3) Yet another function call" << endl;
cout << "n) ..." << endl;
cout << "0, to exit" << endl;
cin>>Op;
switch (Op)
{
case 1:
{
add();
}
default:
{
break;
}
}
}
while (Op != 0);
}

Answer 1

Most easiest option would be to handle exit point in one of the
Switch case statement as follows.
*** Also don't forget to add break statement after every case statement
switch (Op)
{
case 1:
add();
break ;
case 0:
return 0 ;
break ;
default:
cout << "Invalid option" << endl;
break;
}
Thanks

Answer 2

Well, I tried to write a small sample program as per your description. I am not sure if it will work on Visual Studio. I compiled it on MacOS using g++. The below code may not be a good way of writing a program, but it sort of works, and maybe helpful for your cause.
I modified your code to make a simpler program for better understanding -
#include <signal.h>
#include <stdlib.h>
#include <iostream>
int sum = 0;
int main(); // Prototyping main() is also not recommended
void siginthandler(int param)
{
std::cout << "[INTERRUPT] Sum so far => " << sum << "\n";
main(); // main() shouldn't be called here, but rather some menu function
}
void add()
{
std::cout << "Addition\n";
std::cout << "Enter a number : ";
int NumA;
std::cin >> NumA;
sum += NumA;
std::cout << "[ADD] Sum so far => " << sum << "\n";
}
int main()
{
// Register the SIGINT handler with the main()
signal(SIGINT, siginthandler);
int Op;
do
{
std::cout << "Main" << std::endl;
std::cout << "1) Add" << std::endl;
std::cout << "2) Another function call" << std::endl;
std::cout << "0, to exit" << std::endl;
std::cin>>Op;
switch (Op)
{
case 1:
{
add(); break;
}
default:
{
break;
}
}
}
while (Op != 0);
std::cout << "[MAIN] Sum so far => " << sum << "\n";
exit(0);
}
It does compile on g++, so I am not sure if it will work for your case or not.
Below is the output I got by executing the program :
Abhinavs-MacBook-Pro:test abhinav$ ./a.out
Main
1) Add
2) Another function call
0, to exit
1
Addition
Enter a number : 34
[ADD] Sum so far => 34
Main
1) Add
2) Another function call
0, to exit
1
Addition
Enter a number : 56
[ADD] Sum so far => 90
Main
1) Add
2) Another function call
0, to exit
^C[INTERRUPT] Sum so far => 90
Main
1) Add
2) Another function call
0, to exit
0
[MAIN] Sum so far => 90
Abhinavs-MacBook-Pro:test abhinav$
I hope the above code helps. May the force be with you..!! :)