C++ String excercise with random numbers

Question

I have to do this excercise:

A common punishment for school children is to write out the same sentence multiple times. Write a C++ stand-alone program that will write out the following sentence one hundred times: “I will always use objectoriented design.” Your program should number each of the sentences and it should “accidentally” make eight different random-looking typos at various points in the listing, so that it looks like a human typed it all by hand.

My knowledge is limited with C random numbers. I have tried this with no success. I can't get 8 errors. As we can see, I get Random errors with the "typo".

Here is my buggy code:

#include <iostream>
#include <ctime>
using namespace std;

int main()
{
    string strPunish = "I will always use objectoriented design.";
    int randFrom = 1;
    int randTo = 100;
    int typoCounter = 0;
    srand(time(NULL));
    int randNumber = randFrom + ( std::rand() % ( randTo - randFrom + 1 ) );
    for (int i = 1; i <= 100; i++)
    {
        if ((i == randNumber) && (typoCounter != 8))
        {
            randFrom = i;
            randNumber = randFrom + ( std::rand() % ( randTo - randFrom + 1 ) );
            string strTypo = strPunish;
            int randTypo = 0 + ( std::rand() % ( strTypo.length() - 0 + 1 ) );
            strTypo.insert(randTypo, "TYPO");
            cout << i << ": " << strTypo << endl;
            typoCounter++;
        }   
        else
            cout << i << ": " << strPunish << endl;
    }
    return EXIT_SUCCESS;
}

Answer 1

As said above, since it is your homework, you should solve it on your own. But I would give you some leads on possible improvements to your code:

1. First and foremost, you should divide your code into small functions - it will make it more readable, and easier to follow!
2. It is easier to create an array with all the numbers in range [0, 99], shuffle it, and just pick the first X lines to mangle (where X can be anything!). Look at std::array and std::shuffle for more information.
3. Don't use hard-coded numbers in your code! You should instead define constexpr variables - it will make your code more readable (remember (1) ?)
4. Extra: It is no longer common to use rand and srand, instead, it is better to use std::mt19937 from <random>. Also, it is more common to see usage of <chrono> instead of <ctime>.

Remark: Notice that you need to be sure that the line numbers you pick to mangle are unique; The fastest way to ensure it (which may not be stuck forever) is to do what I have suggested in (2).

Answer 2

I've made the entire program for you:

#include <iostream>
#include <ctime>

void selectionSort(int[], int);

int main(void)
{
    std::string punishStr = "I will always use objectoriented design."; // declaration
    std::string tempStr = punishStr;
    std::string typoStr = "TYPO";
    int length = punishStr.length();
    int location = 0;
    short int count = 0;
    int randoms[8] = {0};

    srand(time(0)); // generates random different times

    for (int i = 0; i < 8; i++)
    {
        randoms[i] = (rand() % 100) + 1; // creates 8 random numbers
    }

    selectionSort(randoms, 8); // sorts random numbers, for sake of being unbiased

    for (int i = 0; i < 100; i++)
    {
        if (randoms[count] == i && count <= 8) // random number equals i
        {
            punishStr = tempStr;
            location = (rand() % length) + 1;
            std::cout << (i + 1) << ": " << punishStr.insert(location, typoStr) << std::endl;
            count++;
        }
        else
            std::cout << (i + 1) << ": " << tempStr << std::endl;
    }

    return 0;
}

void selectionSort(int a[], int n) // sorting algorithm
{
    int i, j, min, temp;

    for (i = 0; i < n - 1; i++)
    {
        min = i;
        for (j = i + 1; j < n; j++)
            if (a[j] < a[min])
                min = j;

        temp = a[i];
        a[i] = a[min];
        a[min] = temp;
    }
}

The program firstly declares some necessary variables including the required eight random numbers with zero. Then, by using the For loop, it redefines all the 8 array elements ranging random numbers between 1-100.

After that, simply it sorts the arrays (otherwise it'll get biased e.g. 54, 32...), to prevent it, we simply sorted it like 32, 54 ... . Thereafter, it checks whether the counter variable is <= 8, if it is, then increment and show the typo sentence. Otherwise, show correct sentence.

It'll repeat over and over again until i is lesser than 100.

Hope it works for you.

Note: Output's so big, better you check that by your own. :-)