how do you do a integer validation in C++? - c++

Question

ok, I have been looking for days now but I cant find anything that will work.
I have a program and I want to make sure that the user enters a integer and not a double.
this program works fine but I need to validate the numOne and numTwo to make sure they are integers and not doubles, (5.5)
int main()
{ //This is where my variables are stored
int numOne, numTwo, answer, rightAnswer, ranNumOne, ranNumTwo;
//this will display to the user to enter a range of numbers to be used
cout << "Please enter a set of numbers to be the range for the problems." << endl;
cout << "Please enter the beginning number." << endl;
cin >> numOne;
cout << "please enter the ending number." << endl;
cin >> numTwo;
//this makes sure that the user entered a integer(if not the program will close)
if (!(cin >> numOne))
{
cout << "You did not enter a integer PLEASE RE-RUN THE PROGRAM AND TRY AGAIN!" << endl;
cin.clear();
cin.ignore(100, '\n');
exit(0);
}
cout << "please enter the ending number." << endl;
cin >> numTwo;
//this makes sure that the user entered a number(if not the program will close)
if (!(cin >> numTwo))
{
cout << "You did not enter a integer PLEASE RE-RUN THE PROGRAM AND TRY AGAIN!" << endl;
cin.clear();
cin.ignore(100, '\n');
exit(0);
}
//this is where the first number is generated
srand(time(0));
ranNumOne = rand() % (numOne - numTwo) + 1;
system("PAUSE");
//this is where the second number is generated
srand(time(0));
ranNumTwo = rand() % (numOne - numTwo) + 1;
//this is where the calculations are done
rightAnswer = ranNumOne + ranNumTwo;
//this displays the problem that was generated
cout << "What is: " << endl;
cout << setw(11) << ranNumOne << endl;
cout << setw(6) << "+" << setw(3) << ranNumTwo << endl;
cout << " -------\n";
cin >> answer;
//this checks to see if the answer is right or not and displays the result
if (answer == rightAnswer)
{
cout << "Your answer was correct! " << endl;
}
else
cout << "The correct answer is: " << rightAnswer << endl;
return 0;
}

Answer 1

Use std:n:ci.fail() to see if it failed.
int numOne;
cin >> numOne;
if(cin.fail())
cout << "Not a number...")
Maybe even a nice template function.
template<typename T>
T inline input(const std::string &errmsg = "") {
T var;
std::cin >> var;
while (std::cin.fail()) {
std::cin.clear();
std::cin.ignore(256, '\n');
std::cout << errmsg;
std::cin >> var;
}
return var;
}
Or not:
#include <iostream>
#include <cstdlib>
#include <iomanip>
#include <string>
#include <ctime>
#define DIFF(n1, n2) (n1 > n2 ? n1 - n2 : n2 - n1)
using namespace std;
int input(const string &firstmsg = "", const string &errmsg = "") {
int var;
std::cout << firstmsg;
std::cin >> var;
while (cin.fail()) {
cin.clear();
cin.ignore(256, '\n');
cout << errmsg;
cin >> var;
}
return var;
}
int main(){
//This is where my variables are stored
int numOne, numTwo, answer, rightAnswer, ranNumOne, ranNumTwo;
//this will display to the user to enter a range of numbers to be used
cout << "Please enter a set of numbers to be the range for the problems." << endl << endl;
numOne = input("Please enter the beginning number: ", "Invalid. Enter again: ");
//this asks the user for the second number
numTwo = input("Please enter the ending number: ", "Invalid. Enter again: ");
//this is where the first number is generated
srand(time(0));
ranNumOne = rand() % (DIFF(numOne, numTwo)) + 1; // ensures it will always be positive
system("PAUSE");
//this is where the second number is generated
srand(time(0));
ranNumTwo = rand() % (DIFF(numOne, numTwo)) + 1;
//this is where the calculations are done
rightAnswer = ranNumOne + ranNumTwo;
//this displays the problem that was generated
cout << "What is: " << endl;
cout << setw(11) << ranNumOne << endl;
cout << setw(6) << "+" << setw(3) << ranNumTwo << endl;
cout << " -------\n";
cin >> answer;
//this checks to see if the answer is right or not and displays the result
if (answer == rightAnswer){
cout << "Your answer was correct! " << endl;
}
else
cout << "The correct answer is: " << rightAnswer << endl;
return 0;
}

Answer 2

why not, get the number into a double and then see if that double is an int. ie
double d;
cin>>d;
if (ceil(d) != d)
cout >> " not an integer";