Why is my If/Else statment block not executing completely? - c++

Question

I'm doing a simple project for my CS class. The goal is to have a person input the amount of each fruit (apples, bananas, oranges) they are purchasing, and the program calculates the total and presents an invoice at the end. My Professor wants us to also include an input check, to verify that the input is a number between 0 and 100. to do this, I have this section of code.
string name;
int apples, oranges, bananas;
int FRUIT_MAX = 100;
int FRUIT_MIN = 0;
float appleCost, orangeCost, bananaCost,
subTotal, tax, total;
cout << "Welcome to Bob's Fruits, what is your name..." << endl;
getline(cin, name);
cout << "How many apples would you like" << endl;
cin >> apples;
cout << endl;
//checking if user entered a number for apples
if (apples >= FRUIT_MIN && apples <= FRUIT_MAX)
{
cout << "Thanks" << endl;
}
else //makes the user retype entry if invalid
{
cout << "Please input a number thats 0 or greater than 0. " << endl;
cin >> apples;
cout << endl;
}
cout << "How many oranges would you like" << endl;
cin >> oranges;
if (oranges >= FRUIT_MIN && oranges <= FRUIT_MAX) //checking to see if number is good
cout << "Thanks" << endl;
else //makes the user retype entry if invalid
{
cout << "Please input a number thats 0 or greater than 0." << endl;
cin >> oranges;
cout << endl;
}
cout << "How many bananas would you like" << endl;
cin >> bananas;
if (bananas >= FRUIT_MIN && bananas <= FRUIT_MAX)
cout << "Thanks";
else
{
cout << "Please input a number thats 0 or greater than 0.";
cin >> bananas;
cout << endl;
}
When I enter a value between 0-100, I receive the proper "thanks" output and then it moves on to the next question. When I enter a number outside of 0-100, the else statement triggers sucsessfully, and the program asks for a number between 0-11.
The problem is when a letter is input. If a letter is input, the program skips through every remaining line, ignoring any additional cin commands, and displays the formatted invoice with all negative numbers. Any ideas why this is happening?

Answer 1

When cin gets an invalid value, it sets a failbit.
int n;
cin >> n;
if(!cin)
{
//not a number, input again!
}
You need to use cin.ignore() so that the input will be 'reset' and request the input again.

Answer 2

you can change the cin part into
while (!(cin>>apples)) {
cout<<"Type Error"<<endl;
cin.clear();
cin.sync();
}

Answer 3

The Problem ist that you do not check for proper type of your input.
Your apples variable is an Int. So as long as a user enters an Int everything will be fine.
But what happens if he or she enters a Char ?
The answer is as one of the guys before me mentioned is that the cin operation will fail.
What can you do to prevent or better to say handle this situation:
#include<iostream>
using namespace std;
int main(int argc , char** argv) {
int apples = 0; //Its always good to initialise a var with a value
cout << "Please enter a number: " << endl;
cin >> apples;
if(!cin) {
cout << "Not a number!" << endl;
// Handle the error
}
else {
cout << "A number was entered" << endl;
}
return 0;
}
Instead of checking for !cin you can also use cin.fail() which will be true if the last cin operation failed.
If you want to read more about cin or inputstreams in generell I would advise you to take a look at the C++ reference.