C++ Vector subscript out of range Line 1201 - c++

Question

I am working on a program that takes in grades from the user and returns the max, min, avg, median, and standard deviation. I keep encountering this error whenever I try to run my code:
File: c:\program files (x86)\microsoft visual studio 12.0\vc\include\vector
Line: 1201
Expression: Vector subscript out of range
Could someone tell me what I'm doing wrong? No matter what I do, I can't seem to fix it. Completely new to coding in C++, so if you could explain in-depth that would be extremely helpful.
This is the block of code it is referring to in the vector file:
#if _ITERATOR_DEBUG_LEVEL == 2
if (size() <= _Pos)
{ // report error
_DEBUG_ERROR("vector subscript out of range");
_SCL_SECURE_OUT_OF_RANGE;
}
Specifically pointing to this line:
_DEBUG_ERROR("vector subscript out of range");
My code:
#include <iostream>
#include <vector>
#include <string>
using namespace std;
void enterGrades()
{
int count = 0;//initialize count
int grade;//initialize grade variable
int maxGrade = 0;
vector<int> gradeList;//initialize vector
vector<int>::iterator gradeListIt;//initialize iterator
do {
cout << "Enter grades [0 to exit]: ";//enter grades
cin >> grade;//user input
count += 1;//for each grade, increase count
gradeList.push_back(grade);//append grades to vector
} while (grade != 0);
};
int maxNum(vector<int> gradeList)
{
int largest = gradeList[0];//initialize largest number
int length = gradeList.size();
gradeList.resize(length);
for (int value = 0; value < length; value++)//traverse vector
{
if (gradeList[value] > largest)//if current value > largest
largest = gradeList[value];//set largest to that value
}
return largest;//return largest
};
int minNum(vector<int> gradeList)
{
int smallest = gradeList[0];
int length = gradeList.size();
gradeList.resize(length);
for (int value = 0; value < length; value++)
{
if (gradeList[value] < smallest)
smallest = gradeList[value];
}
return smallest;
};
int avgNum(vector<int> gradeList)
{
int total = 0;
int length = gradeList.size();
gradeList.resize(length);
for (int value = 0; value < length; value++)
{
total += value;
}
return total / length;
};
//int stdDev (vector<int>& gradeList)
//{
// int variance = 0;
// int avg = avgNum(vector<int>& gradeList);
// int length = gradeList.size();
// for(int value = 1; value < length; value++)
// {
// variance = variance + pow(value - avg, 2);
// }
// variance = pow(variance / length, 0.5);
// return variance;
//
//};
int main()
{
vector<int> gradeList;//initialize vector
vector<int>::iterator gradeListIt;//initialize iterator
enterGrades();//
cout << "Maximum grade is: " << maxNum(gradeList) << endl;
cout << "Minimum grade is: " << minNum(gradeList) << endl;
cout << "Average grade is: " << avgNum(gradeList) << endl;
}
Also, in my main function; can I call other functions like I did in my output statements?

Answer 1

Giving things the same name doesn't make them the same thing.
After enterGrades returns, the vector named "gradeList" in main is still empty.
When you try access the first element of an empty vector, you get an error.
Your main should look like this:
int main()
{
std::vector<int> gradeList = enterGrades();
cout << "Maximum grade is: " << maxNum(gradeList) << endl;
cout << "Minimum grade is: " << minNum(gradeList) << endl;
cout << "Average grade is: " << avgNum(gradeList) << endl;
}
Changing the implementation of enterGrades to fit is left as an exercise.
Also, this thing that you keep doing:
int length = gradeList.size();
gradeList.resize(length);
doesn't make sense, as it's resizing a vector to the size it already had.
Remove it.
You're also repeatedly declaring an iterator for no reason at all.
You also probably want to review what average you're supposed to calculate, as you're calculating the average index in a vector, not the average value.
And watch out for those integer divisions.