为什么对于程序的大值而不是小值，程序崩溃？

Question

Why do I get a program crash for large values but not small values for my program? If I input 1-3 the program does what it is supposed to but when I enter a number greater than that the program crashes and/or does not complete? Is it something to do with a pointer error or the way I've referenced something? I'm unsure so any help is appreciated. Thanks!

Code:

#include <iostream>
using namespace std;

void getData (int size, int *Arr){

    cout << "\n\nEnter integer data one line at a time\n" << endl ;

    for (int i=0; i < size; i++){
        cin >> Arr[i];
    }
}

void findMinAndMax(int array[], int size, int *min, int *max) {

    int smallest = array[0];
    int largest = array[0];

    *min = smallest;
    *max = largest;

    for (int i = 1; i < size; i++)
        {
            if (array[i] > *max){
                *max = array[i];
                cout << "Max Value (loop): " << *max << endl;
            }
            if (array[i] < *min){
                *min = array[i];
                cout << "Min Value (loop): " << *max << endl;
            }
        }

    // testing code
    cout << "Min Value: " << *min << endl;
    cout << "Max Value: " << *max << endl;

}

int *makeFrequency (int data[], int dSize, int *minDataValue, int *maxDataValue) {

    cout << "Min Value Pre: " << *minDataValue << endl;// testing code
    cout << "Max Value Pre: " << *maxDataValue << endl;// testing code
    findMinAndMax(data, dSize, minDataValue, maxDataValue);
    cout << "Min Value Post: " << *minDataValue << endl; // testing code
    cout << "Max Value Post: " << *maxDataValue << endl;// testing code


    int fSize = *minDataValue + *maxDataValue;

    cout << "fSize: " << fSize << endl; // testing code

    int *frequency;
    frequency = new int [fSize];

    // if frequency is 0, end
    if (frequency == 0)
        {
            return 0;
        }

    // set all elements to 0 in array frequency
    for (int i = 0; i <= fSize; i++) {
        frequency[i] = 0;
    }


    for (int i = 0; i <= dSize; i++) {
        int j = data[i] - (*minDataValue) + 1;
        frequency[j] = frequency[j] + 1;
    }

    return frequency;
}

void makeHistogram (int *freq, int min, int max ){

    cout << "Frequency Value HISTOGRAM: " << *freq << endl;

    cout << "\n\n\n ----------- Histogram ----------------\n" << endl;

    int size = min + max;
    cout << "Size Value HISTOGRAM: " << size << endl;

    for (int i = 0; i < size; i++){

        if (freq[i] > 0) {

            cout << "\n" << min + i - 1 << ": ";

            for (int j = 0; j < freq[i]; j++) {
                cout << '*';
            }
        }
    }
    cout << endl << endl;
}

int main() {

    int dSize;
    int *ArrayOfInts;

    cout << "How many data values? ";
    cin >> dSize;

    ArrayOfInts = new int [dSize];

    getData(dSize, ArrayOfInts);


    int *frequency, min, max;

    frequency = makeFrequency(ArrayOfInts, dSize, &min, &max);

    if (frequency == 0) return -1;

    cout << "Min Value MAIN: " << min << endl; // testing code
    cout << "Max Value MAIN: " << max << endl; // testing code
    cout << "Frequency Value MAIN: " << *frequency << endl;

    makeHistogram(frequency, min, max);


    delete [] frequency;

    return 0;
}

Answer 1

One place where you have undefined behaviour which can cause crashes:

here you allocate fSize elements:

frequency = new int [fSize];

later you iterate it until fSize :

for (int i = 0; i <= fSize; i++) {

you should change to i < fSize , because there is no fSize element in your array. And the same problem with i <= dSize later on. Should be i < dSize .

btw. I dont see why only large values should cause crashes in your code, maybe this is just UB.

Answer 2

You're setting fSize incorrectly. It should be the difference between the maximum and minimum values, not the sum of them. Otherwise, if you have negative numbers in your list, the frequency array will be too small. And if absolute value of any of the negative numbers is larger than the highest number, fSize will be negative, which is not valid for the size of an array.

Then you need to add 1 to include both endpoints. So it should be:

int fSize = *maxDataValue - *minDataValue + 1;

Then, as the other answer pointed out, you need to fix your for loops. When the size of an array is N , the array indexes from from 0 to N-1 . So it should be:

for (int i = 0; i < fSize; i++) {

using < as the loop test, not <= . If you try to write outside an array, you invoke undefined behavior, so anything can happen -- if you're lucky you get a crash, but that's not guaranteed.

You have a similar problem when you assign to frequency :

for (int i = 0; i <= dSize; i++) {
    int j = data[i] - (*minDataValue) + 1;
    frequency[j] = frequency[j] + 1;
}

There's no need to add 1 when subtracting *minDataValue , and doing so will cause you to go outside the array when data[i] is the maximum.