Count the occurrence of numbers in C++?

Question

I just recently created a code in C++ where I have to display the occurrence of numbers from a text file that I made using this code:

using namespace std;

int main()
{

    bool isCovered[99] = {};
    int number;


    // Read each number and mark its corresponding element covered
    while (cin.good())
{
    cin >> number;
    if (number == 0)
    {
        break;
    }
    if ((number >= 1) && (number <= 99))
    {
        isCovered[number - 1] = true;
    }
}


    // Check if all covered
    bool allCovered = true; // Assumes all covered initially
    for (int i = 0; i < 99; i++)
        if (!isCovered[i])
        {
            allCovered = false; //Finds one number not covered
            break;
        }
    // Display result
    if (allCovered)
     cout << "The tickets cover all numbers" << endl;
    else
     cout << "The tickets don't cover all numbers" << endl;

    return 0;
}

It's not displaying a result, is the program too complex, or is it something that I'm missing?

EDIT: Thanks @selbie for the edit to my code, i was able to figure out that it was a user input but when i put in a zero for the final input. It displays the messages "The tickets don't cover all numbers", why is that?

You don't need a loop to initialize all items in `isCovered` to false. You can simply declare `bool isCovered[99] = {};` — selbie, Jan 16 '20 at 01:30
If you need to count the number of occurrences it would make more sense to hold an array of integers so that `count[number - 1]` will give you the frequency of `number`. And just do `count[number-1]++` to count. — David G, Jan 16 '20 at 01:32
I get perfectly sensible results when I run that program. Exactly what input did you give it? — abelenky, Jan 16 '20 at 01:34
Adding onto abelenky's comment, example output that you are seeing alongside the output you expect to see would be helpful in determining the root cause of the problem. — Skyler Ferris, Jan 16 '20 at 01:36
Alright @selbie, i went and removed the ```// Initialize the array``` part and added the ```{}``` but repl.it is still showing a blank result. — Big Pete, Jan 16 '20 at 01:36
Ok @0x499602D2, @abelenky, i was able to input the numbers into the ```{}``` but it came up with this error message: ```main.cpp:7:41: error: constant expression evaluates to 45 which cannot be narrowed to type 'bool' [-Wc++11-narrowing] ...= {5, 78, 8, 9, 70, 45, 8};``` what could it mean? I'm still learning C++ as a student. — Big Pete, Jan 16 '20 at 01:43
If you type any number into your input stream greater than `99`, you'll get undefined behavior. — selbie, Jan 16 '20 at 01:52
@BigPete `{5, 78, 8, 9, 70, 45, 8}` -- Where did this new code come from? Also, as suggested, you need to check if anything greater than 99 is entered — PaulMcKenzie, Jan 16 '20 at 01:54
What do you mean by not displaying anything? Is console blank? What is the input? — TruthSeeker, Jan 16 '20 at 01:54
@PaulMcKenzie i have a series of numbers in a text file that i'm trying to get the program to run. But they are not puncuated (basically without commas). — Big Pete, Jan 16 '20 at 01:59
Pete, are you manually typing your numbers into the console to test, or are you using file redirection (ala: `program.exe < input.txt` ) ? — selbie, Jan 16 '20 at 02:00
@BigPete In your comment, you highlighted the error as if that text is within your code. All you were told to do is `bool isCovered[99] = {};` — PaulMcKenzie, Jan 16 '20 at 02:00
Then, problem could be the reading file or somewhere else. Please provide [minimum reproducible exams](https://stackoverflow.com/q/5963269/4139593) — TruthSeeker, Jan 16 '20 at 02:07
@selbie i'm not too sure. I'll see if i can keep messing around with it. — Big Pete, Jan 16 '20 at 02:29
This sounds like a task for `std::map` or even just `std::set`, rather than an array — Remy Lebeau, Jan 16 '20 at 05:43

selbie · Answer 1 · 2020-01-16T08:35:09.843

The bug, if any, is here:

cin >> number;
while (number != 0)
{
    isCovered[number - 1] = true;
    cin >> number;
}

Two possible issues:

If reading from a redirected file, there's no detection of an end-of-file condition. Such would be the case if the program was invoked as program.exe < input.txt and the input.txt did not contain a 0. Without checking for eof, the program will hang when reading from an input file redirection.
Further, there's nothing to guard against bad input. i.e. numbers outside the range of [1..99]. Without guarding against out of range numbers, undefined behavior will get introduced. Or more likely, the stack will get trashed as a result of inserting into a memory address out of range.

The easy fix is this:

while (cin.good())
{
    cin >> number;
    if (number == 0)
    {
        break;
    }
    if ((number >= 1) && (number <= 99))
    {
        isCovered[number - 1] = true;
    }
}

` // Read each number and mark its corresponding element covered while (cin.good()) { cin >> number; if (number == 0) { break; } if ((number >= 1) && (number <= 99)) { isCovered[number - 1] = true; } }` So, i was able to change it but didn't realize that i had to manually input my numbers in the system, lol, i also noticed that when i put `0` in for my final input it gave me `cout << "The tickets don't cover all numbers" << endl;` — Big Pete, Jan 16 '20 at 17:32

Count the occurrence of numbers in C++?

1 Answers1