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Stuck in an endless loop

When I run this program for a class, I get stuck in an infinite loop whenever I enter '|' to end the while loop. I feel like I am missing something obvious.

This issue is on page 126 of Bjarne Stroustrup's C ++ Programming book, but as a quick estimate, I just have to find the largest and smallest numbers that the user has typed and return information about it. Entering in '|' has to break out of the loop so I can go to the part where it gives information about all the numbers entered, but whenever I type that character (or any character, not a number) it creates an infinite loop.

Here is my code.

int main()
{
    vector<double> nums;

    while (true)
    {
        double current_num;
        cout << "enter a double \n";
        cin >> current_num;
        if (current_num == '|')
            break;
        nums.push_back(current_num);
        sort(nums.begin(), nums.end());
        cout << nums[nums.size()-1] << " is the largest so far.\n";
        cout << nums[0] << " is the smallest so far.\n";
    }
    cout << nums[nums.size()-1] << " is the largest number.\n";
    cout << nums[0] << " is the smallest number.\n";
    cout << "Number of values entered: " << nums.size() << '\n';
    double sum = 0;
    for (int k = 0; k<nums.size(); ++k)
        sum += nums[0];
    cout << "Sum of all values: " << sum << '\n';
    for (int j=0; j<nums.size(); ++j)
        cout << nums[j] << ' ';
    return 0;
}

I used VS13 in class and didn't have this problem, but now I am coding in notepad ++ and using PuTTY to compile at home (although I doubt it has anything to do with it).

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4 answers


You are comparing a character to double

here:

if (current_num == '|')

And this comparison will never do what you want.

Read the symbol first, compare it to '|'

, then double-convert it if necessary.



Note:

For your entry, the ASCII value '|'

is 124, so if you enter 124 your loop ends ...

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you are comparing a number to a character.

if (current_num == '|')


current_num

contains the number in the double that you are trying to compare to the char that '|'

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Because you are trying to insert not a number into a double. I believe in your case you should read the input into a string / char and parse it.

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The problem is here:

if(current_num == '|'){
}

Instead, read in std::string

and parse it to double.

Thus, the modified snippet will look something like this:

while (true)
    {
        string strNum;
        double current_num;
        cout << "enter a double \n";
        cin >> strNum;
        if (strNum == "|")
            break;
        istringstream strm(strNum);
        strm >> current_num;
        nums.push_back(current_num);
        sort(nums.begin(), nums.end());
        cout << nums[nums.size()-1] << " is the largest so far.\n";
        cout << nums[0] << " is the smallest so far.\n";
    }
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