Exceptional Handling in C++ when user inputs string instead of int - c++

Question

I have a program that requires a user to input a integer number which then has to go to several conditions. When I run the program, if i input a int number it works but if i input a character, the programs just spams the error messages.
I think exception handling might work here but i m not sure how to do.Help out guys!
Here is a part of my prog:
#include <iostream.h>
#include <conio.h>
int i, j, data;
void main()
{
int tempdata;
retry:
cout<<"\n\n Enter the row and coloumn where you want to enter data" <<endl;
cin>>i>>j;
if (i>=1 && i<=9 && j>=1 && j<=9)
{
cout<<"\n Enter your desired value to put in that place"<<endl;
cin>>tempdata;
if(tempdata>=1 && tempdata<=9)
{
data=tempdata;
}
else
{
cout<<"\n Soduku contains numbers from 1 to 9 only.Please try again"<<endl;
goto retry;
}
}
else
{
cout<<"\nEntered row or coloumn is not valid"<<endl;
cout<<"Please try again"<<endl;
goto retry;
}
getch();
}

Answer 1

Instead of a cout, you should indeed use exception handling.
if(tempdata>=1 && tempdata<=9)
{
data=tempdata;
}
else
{
throw std::runtime_error("Soduku contains numbers from 1 to 9 only.Please try again");
}
By putting all this into a function, and not your main, you can then call this function within a try/catch block, and deal properly with the exception: display a pop-up message if you have a GUI, ignore the input, etc. The important part is that, if you ignore it, it is not actually ignored. It is dealt with. Which makes your code a LOT cleaner and maintainable. Example:
try
{
input();
}
catch(std::runtime_error& e)
{
// deal with your invalid input here
}
Also, goto statements are considered bad practice. They can be easily replaced by if/else or while statements, or with return codes in functions. And using them tend to make the code unreadable, difficult to follow.

Answer 2

You need to validate that cin >> is successful before you can then use the value entered. If the user enters data that does not match the expected type, you have to clear the error before you can read new input again.
Try this:
#include <iostream>
#include <limits>
int i, j, data;
bool isNumValid(int data) {
return ((data >= 1) && (data <= 9));
}
void clearInput() {
std::cin.clear();
std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
}
int main() {
int tempdata;
do {
std::cout << "\n\n Enter the row and column where you want to enter data" << std::endl;
if (!(std::cin >> i >> j)) {
std::cout << "\n Please enter numbers only!" << std::endl;
clearInput();
continue;
}
if (!isNumValid(i) || !isNumValid(j)) {
std::cout << "\nEntered row or column is not valid" << std::endl;
std::cout << "Please try again" << std::endl;
continue;
}
std::cout << "\n Enter your desired value to put in that place" << std::endl;
if (!(std::cin >> tempdata)) {
std::cout << "\n Please enter a number only!" << std::endl;
clearInput();
continue;
}
if (!isNumValid(tempdata) {
std::cout << "\n Soduku contains numbers from 1 to 9 only" << std::endl;
std::cout << "Please try again" << std::endl;
continue;
}
data = tempdata;
}
while (true);
std::cin.get();
return 0;
}
Alternatively:
#include <iostream>
#include <limits>
#include <stdexcept>
int i, j, data;
bool isNumValid(int data) {
return ((data >= 1) && (data <= 9));
}
void checkRowColValid(int row, not col) {
if (!isNumValid(row) || !isNumValid(col))
throw std::out_of_range("Entered row or column is not valid");
}
void checkDataValid(int data) {
if (!isNumValid(data))
throw std::out_of_range("Soduku contains numbers from 1 to 9 only");
}
int main() {
int tempdata;
std::cin.exceptions(std::ios_base::failbit);
do {
try {
std::cout << "\n\n Enter the row and column where you want to enter data" << std::endl;
std::cin >> i >> j;
checkRowColValid(i, j);
std::cout << "\n Enter your desired value to put in that place" << std::endl;
std::cin >> tempdata;
checkDataValid(tempdata);
data = tempdata;
}
catch (const std::out_of_range &e) {
std::cout << "\n " << e.what() << std::endl;
std::cout << "Please try again" << std::endl;
}
catch (const std::ios_base::failure &) {
std::cout << "\n Please enter numbers only!" << std::endl;
std::cin.clear();
std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
}
}
while (true);
std::cin.get();
return 0;
}