C++ Comma Separated Input Array Code Exiting Prematurely

Question

I'm trying to create C++ code to take user input separated by a comma and feed it into an int array to then sort it all with even columns. For some reason when I feed it into the array the program shuts on me. I can't even have it print the array, and I'm not quite sure why.

sample:

Welcome to Please Help Me Sort Grades!!! :)
Please enter student grades:10,20,30,10,20,30,50,90,10,50

Unsorted:
  Grade  ID
     10   1
     20   2
     30   3
     10   4
     20   5
     30   6
     50   7
     90   8
     10   9
     50  10

Sorted:
  Grade  ID
     10   1
     10   4
     10   9
     20   2
     20   5
     30   3
     30   6
     50   7
     50  10
     90   8

Process finished with exit code 0

code:

#include <iostream>
#include <cmath>
#include <iomanip>
#include <cstdlib>
#include <ctime>
#include <cstring>
#include <string>
#include <vector>

using namespace std;
// Global Variables and Libraries are declared


using namespace std;


int main() {

    cout << setprecision(20) << fixed;

    int size = 30;
    int StudentID[size];
    int StudentGrades[size];
    string commaList;
    vector<int> grades;
    int MinGrade;
    int MinID;

    //char * token is a char pointer. We will discuss them in a later chapter
    char *token = NULL;

    cout << "Please enter a comma separated list of grades: ";
    getline(cin, commaList);
    //character array that will hold comma seperated list after its copied over
    char gradesCharArr[commaList.size()];
    strcpy(gradesCharArr, commaList.c_str());
    //gives you the location of the first ',' thats encountered in the array
    token = strtok(gradesCharArr, ",");
    //Iterate through each "," that is found until there are none left
    while(token != NULL){
        //convert the grade from a string to an int and push it into the vector
        grades.push_back(stoi(token));
        //find next occurrence of ","
        token = strtok(NULL, ",");
    }

    for(int i = 0; i < size; i++){
        if(i > grades.size()){
            StudentGrades[i] =0;
            StudentID[i] = 0;
        }
        else {
            StudentGrades[i] = grades.at(i);
            StudentID[i] = i + 1;
        }
    }

    cout << "Unsorted: " << endl;
    //Print grades back to show they are properly tokenized
    for(int i = 0; i < grades.size(); i++){
        cout << StudentGrades[i] << setw(10) << StudentID[i] << endl;
    }

    for(int i = 0; i < size; i++)                                               // for the first initial round where we will put the official
    {                                                                           // max number when found (i)
        for(int j = i + 1; j < size; j++)                                       // for the second subround (j) here the code is comparing the max
        {                                                                       // value of the array at j and the array at i until we get
            if(StudentGrades[j] < StudentGrades[i])                                         // the ultimate max number. In order to do that though we will
            {                                                                   // shift the values up one place in the Array and place the
                MinGrade = StudentGrades[i];                                        // max number in it's proper place in MyArray.
                MinID = StudentID[i];
                StudentGrades[i] = StudentGrades[j];
                StudentID[i] = StudentID[j];
                StudentGrades[j] = MinGrade;
                StudentID[j] = MinID;
            }
        }
    }

    cout << "Sorted:" << endl;
    for(int i = 0; i < grades.size(); i++){
        cout << StudentGrades[i] << setw(20) << StudentID[i] << endl;
    }

    return 0;
}

Thank you so much in advance :)

Answer 1

The error spotted by Mateus Melo is correct. There is one more in the for loop for sorting items. The size should be grades.size() in both for statements to sort properly here

  for (int i = 0; i < size; i++)                                               // for the first initial round where we will put the official
  {                                                                           // max number when found (i)
    for (int j = i + 1; j < size; j++)                                       // for the second subround (j) here the code is comparing the max

Replacing with grades.size() should produce expected result :)

Also taking input would be better with this code

  cout << "Please enter a comma separated list of grades: ";
  getline(cin, commaList);
  size_t as = commaList.size();
  //character array that will hold comma seperated list after its copied over
  char* gradesCharArr = new char[as+1]();// [a /*commaList.size()*/] ;
  commaList.copy(gradesCharArr, commaList.size());

Answer 2

In your first for loop, when i is equal to grades.size(), you access a position i of grades that is invalid. Change your if to:

    if(i>=grades.size())

and your code will work just fine.

Answer 3

for(int i = 0; i < size; i++){
    if(i >= grades.size()){
        StudentGrades[i] =0;
        StudentID[i] = 0;
    }
    else {
        StudentGrades[i] = grades.at(i);
        StudentID[i] = i + 1;
    }
}

This is where the problem is. You see, the indices in C++ start with 0. So, when your i becomes grades.size() it goes out of bounds for the vector. That is what the debugger basically told you by the error:

{ __throw_out_of_range_fmt(__N("vector::_M_range_check: __n " "(which is %zu) >= this->size() " "(which is %zu)"), __n, this->size()); }

---

So, you need to change that condition to:

if(i==grades.size())

---

Also, on a side note, when you're using vector indices, it is better to use size_t instead of plain old int, as all vector functions require size_t and if they do not find that, they will give the usual overflow error

Hope this helps :)