Finding Max, Min, Avg using dynamic memory allocation and pointers - c++

Question

I am learning pointers so I tried to implement this simple code of finding Max, min and Avg of student grades.
I only could found the avg BUT for the Max and the Min I got the first element of the *p.
here is my code If you please can tell me what is my mistake
#include <iostream>
using namespace std;
int main()
{
int *p;
int x;
cout << "Enter a number of student: ";
cin >> x;
p = new int[x];
for (int i = 0; i < x; i++)
{
cout << "Enter a grade: ";
cin >> *(p + i);
}
int sum = 0;
int max = 0;
int min = 0;
max = *p;
min = *p;
for (int i = 0; i < x; i++)
{
if (min > *p)
{
min = *p;
p++;
}
}
for (int i = 0; i < x; i++)
{
if (max < *p)
{
max = *p;
p++;
}
}
for (int i = 0; i < x; i++)
{
sum += *p;
p++;
}
int avg = sum / x;
cout << "avg is : " << avg << endl;
cout << "Max num is : "<< max
<< "\n Min num is : " << min << endl;
}

Answer 1

Note the changes
for (int i = 0; i < x; i++)
{
if (min > *(p+i))
{
min = *(p+i);//changed
}
}
for (int i = 0; i < x; i++)
{
if (max < *(p+i))
{
max = *(p+i);//changed
}
}
for (int i = 0; i < x; i++)
{
sum += *(p+i);//changed
}

Answer 2

You only advance the pointer, if *p is greater than the current max or min. Either advance it on every iteration (and back up the original state) or use p[i] to get the element of the iteration.

Answer 3

Your code is wrong on a number of levels. First of all, have a look at how you initialize the pointer p, which is supposed to point to the beginning of your array containing int elements :
p = new int[x];
This is all good. However, if you now take a look at the first loop...
for (int i = 0; i < x; i++)
{
if (min > *p)
{
min = *p;
p++;
}
}
You will notice that you keep incrementing p, which was supposed to point to the beginning of the array. This way, you can't possibly visit every element of the array when you run the second loop, because p does not point at the start of your array anymore! Thus, you invoked what some people call undefined behaviour by accessing an array out of its bounds.
However, you were able to properly reference the array in the loop where you actually write the elements to it - with the line cin >> *(p + i);.
Also, you should always remember to delete everything you newed. However, if you lose the pointer to what new returned, you will never be able to successfully delete it.
Furthermore, if you're programming in C++, you really should avoid using raw pointers, and - if you really need to - wrap them inside an unique_ptr (if you're using C++11). When it comes to "dynamic arrays", std::vector is most often the better way.

Answer 4

That's because you're doing p++, thus "losing the pointer".
In each for loop except for the first one, change *p to p[i], and get rid of the p++.
Also, at the end of the function, call delete p.

Answer 5

You could inline the calculation of max, min, and sum:
int sum = 0;
int max = 0;
int min = 0;
for (int i = 0; i < x; i++)
{
int g=0;
cout << "Enter a grade: ";
cin >> g;
if (g > max)
max = g;
if (g < min)
min = g;
sum += g;
}
Then you wouldn't need p = new int[x]