Why do I get infinite loop instead of exception? - c++

Question

I make a program which will have some functions to work with my structure. I haven't added the functions yet, but I have problems with user interface. When I input "hello" instead of int (for choice & choice2), I expect to get exception but instead I get infinite loop. If "hello" is an array of chars and chars are transferred to corresponding ASCII codes, I don't understand why loop is infinite. I need exception so I can catch it.
#include <iostream>
#include <fstream>
#include <vector>
using namespace std;
#define MARK_AMOUNT 4
struct student{
string name;
string group;
int mark[MARK_AMOUNT];
};
istream& operator >> (istream& in, student& student) {
in >> student.name >> student.group;
for (int i = 0; i < MARK_AMOUNT; i++) in >> student.mark[i];
return in;
}
ostream& operator << (ostream& out, const student& student) {
out << student.name << "\t" << student.group << "\t";
for (int i = 0; i < MARK_AMOUNT; i++) out << student.mark[i] << " ";
return out;
}
int main(){
vector <student> list;
int choice, choice2;
ifstream myfile;
bool input = false, input2 = false;
while(!input){
cout << "Input:\n1 to work with files\n2 to work in console\n";
cin >> choice;
if(choice == 1 || choice == 2) input = true;
else cout << "Wrong number.\n";
}
while(!input2){
cout << "Input function number[1-3]: ";
cin >> choice2;
if(choice2 >= 1 && choice2 <= 3) input = true;
else cout << "Wrong number.\n";
}
switch (choice) {
case 1:
{
string fileName;
cout << "Input name of file: ";
cin >> fileName;
ifstream myfile(fileName);
student temp;
while(myfile >> temp){
list.push_back(temp);
}
}
break;
case 2:
break;
default:
break;
}
switch (choice2) {
case 1:
break;
case 2:
break;
case 3:
break;
default:
break;
}
switch (choice) {
case 1:
{
myfile.close();
break;
}
case 2:
break;
default:
break;
}
return 0;
}
Output:
Input:
1 to work with files
2 to work in console
hello
Wrong number.
Input:
1 to work with files
2 to work in console
Wrong number.
Input:
1 to work with files
2 to work in console
Wrong number.
...
...

Answer 1

If you want execution to continue then you definitely do not need an exception.
You need a mechanism to first check if the input is valid since std::cin goes into an error state and leaves the input in its buffer, thus skipping through the next call.
Here is the sample on wich you can build upon:
#include <iostream>
#include <sstream>
#include <string>
using namespace std;
int main(){
int choice, choice2;
bool input = false, input2 = false;
std::string line;
while(!input){
cout << "Input:\n1 to work with files\n2 to work in console" << endl;
while (std::getline(std::cin, line))
{
std::stringstream ss(line);
if (ss >> choice)
{
if (ss.eof())
{ // Success
break;
}
}
std::cout << "Invalid Input, try again" << endl;
}
if(choice == 1 || choice == 2) input = true;
else {
cout << "Wrong number.\n" << endl;
}
}
}