How to simply validate correctly in c++? [duplicate] - c++

Question

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Closed 4 years ago.
I am new to c++ - and I am having trouble to validate user that the input must be a integer, and I just want the basic - simpler way, for me to understand. (Just basic way) to validate the input of the user How can I make it to work prior to my code below. Thank you for you're help and you're time. For example: if I get prompt to enter positive number and Input the letter x that means it will show "Invalid entry".. thank you!
Here is my code:
Updated
if (cin >> x && x < 0) {
} else {
cout << "Invalid entry, Try again." << endl;
cin.clear();
while (cin.get() != '\n');
}
#include <iostream>
#include <fstream> // for file stream.
using namespace std;
int main() {
// Variables
int x, reversedNumber, remainder;
// Creating String variables and setting them to empty string.
string even = "", odd = "";
// Creating a file.
ofstream out;
out.open("outDataFile.txt");
// creating a character variable
// for the user input if they want to use the program again.
char ch;
do {
// Even number.
even = "";
// Odd number.
odd = "";
// Reversed number
reversedNumber = 0;
// Prompt the user to enter a positive integer.
cout << "\nEnter a positive integer and press <Enter> ";
// Validate user input.
while (cin >> x || x < 1) {
// Clear out the cin results.
cin.clear();
// Display user that it is not a positive integer.
cout << "Invalid entry, Try again. ";
}
// Display Results to the screen
cout << "the original number is " << x << "\n";
// Display results in the text file.
out << "the original number is " << x << "\n";
// Display number reversed.
cout << "the number reversed ";
// Display number reversed in text file.
out << "the number reversed ";
//Reversing the integer.
while (x != 0) {
remainder = x % 10;
reversedNumber = reversedNumber * 10 + remainder;
// Display on screen
cout << remainder << " ";
// Display in text file.
out << remainder << " ";
x /= 10;
}
// Display the results on screen and in the text file.
cout << "\n";
out << "\n";
// Reading the reverse numbers result.
while (reversedNumber != 0) {
remainder = reversedNumber % 10;
// Checking if the number is even or odd.
if (remainder % 2 == 0) {
// even = even * 10 + remainder;
} else {
// odd = odd * 10 + remainder;
}
reversedNumber /= 10;
}
//Displaying the even numbers.
if (even != "") {
cout << "the even digits are " << even << "\n";
out << "the even digits are " << even << "\n";
}
// If it is not even then display..
else {
cout << "There are no even digits \n";
out << "There are no even digits \n";
}
//Display the odd results.
if (odd != "") {
cout << "the odd digits are " << odd << "\n";
out << "the odd digits are " << odd << "\n";
}
// If its not odd then display.
else {
cout << "There are no odd digits \n";
out << "There are no odd digits \n";
}
// just a divider to divide the results inside text file.
out << "----------------- \n";
// Prompt the user if they want to use the program again.
cout << "\nDo you like to continue/repeat? (Y/N):";
// get the input from user.
cin >> ch;
if ((ch == 'Y') || (ch == 'y')) {
} else {
cout << "\nGoodbye!" << endl;
}
} while (ch == 'y' || ch == 'Y');
// close the text file.
out.close();
return 0;
}

Answer 1

You could read a string from cin and check each character to make sure that when passed to isdigit() it returns true.
std::string x;
std::cin >> x;
for(char c : x){ //for each char c in string x
if(!isdigit(c)) //Invalid
}