help using push_back

I need help using the push_back operation. See code.

Code:

---

#include <iostream>
#include <iomanip>
#include <cstdlib>
#include <ctime>
#include <vector>

using namespace std;

double FillVec (vector <int> &);
void PrintVec (vector <int>);
double Average (vector <int>);
int FindLargest (vector <int>);
void Exchange (vector <int> &, int);

int main (void)
{
        vector <int> Vec1 (100);
        vector <char> CharVec [26];
        float Ary1 [10];
        int IndexOfLargest, TheNum = 0;
       
        srand (time(NULL));

        FillVec(Vec1);

        cout << "The average is " << setiosflags(ios::fixed) << setprecision(2) <<
                Average (Vec1) << endl << endl;
       
        PrintVec (Vec1);

        FindLargest (Vec1);

        cout << "The largest element is " << setiosflags(ios::fixed) << setprecision(2) <<
                FindLargest(Vec1) << endl << endl;

        Exchange (Vec1, IndexOfLargest);

        PrintVec(Vec1);

        return 0;
}
double FillVec (vector <int> & ivec)
{
        int Total = 0;
        int Size;

        vector <int> MyVec (100);
       
        if (ivec.size() != 0)
        {
                MyVec = ivec;
                Size = ivec.size();
        }
        else
                Size = 100;

        for (int i = 0; i < Size; i++)
        {
                MyVec[i] = rand() % 199 - 99;
                Total += MyVec[i];
        }

        ivec = MyVec;

        return (double(Total) / ivec.size());

}
void PrintVec (vector <int> ivec)
{
        for (int index = 0; index < ivec.size(); index++)
        {
                cout << setw(5) << ivec[index];

                if (index % 10 == 9)
                        cout << endl;
        }

        cout << endl;
}
double Average (vector <int> ivec)
{
        int sum = 0;
        int Size = ivec.size();

        for (int index = 0; index < Size; index++)
                sum += ivec [index];

        return (double (sum) / Size);
}
int FindLargest (vector <int> ivec)
{
       
        int maxIndex = 0;

        for (int index = 1; index < 100; index++)
                if(ivec[maxIndex] < ivec[index])
                        maxIndex = index;

                return ivec[maxIndex];
}
void Exchange (vector <int> & ivec, int i)
{
       
        ivec.push_back(100);

        for (i = 0; i < 100; i++)
        ivec[i];
       
}

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After finding the largest element of Vec1 and printing it out. Exchange is supposed to exchange the largest element of Vec1 with the last element of the vector. Am I using push_back correctly? I read through the section in my book about push_back, but I'm still unsure. My output just puts the number 100 at the end of the vector.
Thank You,
Kristina

No. push_back() inserts one element into a vector.

// Insert one element
ivec.push_back(100);

// Here you are trying to access 100 elements.
for (i = 0; i < 100; i++)
ivec[i];

Kuphryn