Search in Dynamic Array - c++

Question

When I'm searching an integer in my dynamic array, the search function isn't working well as its always showing its positioned at 1. whether the data is actually there or not.
What i'm actually trying to do is using dynamic data structure, I'm adding the data. Deleting, searching and saving to txt file. and Loading it back. But the problem is search. I used switch cases and search is at Case 4.
#include<iostream>
#include<string>
#include<fstream> //to save file in text
using namespace std;
int main()
{
int *p1;
int size = 0;
int counter = 0;
p1 = new int[size];
int userchoice;
int i;
int position;
while (1)
{
cout << "Please enter your choice " << endl;
cout << endl;
cout << "To insert Press '1'" << endl;
cout << "To Delete press '2'" << endl;
cout << "To View press '3'" << endl;
cout << "To Search press '4'" << endl;
cout << "To Save Press '5'" << endl;
cout << "To Load Previously saved Data press '6'" << endl;
cout << "To Exit press '7'" << endl;
cout << endl;
cout << "Enter your choice: ";
cin >> userchoice;
switch (userchoice) // User's selection from the menu
{
case 1: //Insert Number
cout << "Enter a Number: ";
cin >> p1[size];
counter++;
size++; //Add's memory space
break;
case 2: //Delete Number
int udelete;
cout << "Enter a number to delete: ";
cin >> udelete; //User enters Number to be deleted
//Checking if the number is in an array.
for (position = 0; position<size; position++)
{
if (p1[position] == udelete)
break;
}
if (position>size)
{
cout << "The number is not in the memory: ";
cout << endl;
break;
}
for (i = position; i<size; i++) {
p1[i] = p1[i + 1];
}
size--;
cout << "Successfully Deleted!!! ";
cout << endl;
break;
case 3: // View
for (i = 0; i<size; i++)
{
cout << "Your data" << " " << i << " " << "-->" << p1[i] << endl;
}
break;
case 4:
{
int usearch;
cout << "Please enter the figure you would like to search ";
cout << "->";
cin >> usearch;
for (i = 0; i>size; i++)
{
if (p1[size] == usearch)
break;
}
if (usearch == size)
{
cout << "not found. ";
}
cout << "Position at: " << i + 1 << endl;
break;
}
case 5: // Save
{
ofstream save;
save.open("Dynamicdata.txt", ofstream::out | ofstream::app);
for (i = 0; i<size; i++)
{
save << p1[i] << endl;
}
save.close();
cout << "File Saved " << endl;
break;
}
case 6: //Read from File
{
string read;
ifstream file_("Dynamicdata.txt");
if (file_.is_open())
{
while (getline(file_, read))
{
cout << read << "\n";
}
file_.close();
}
else
cout << "File Not open" << endl;
cin.get();
break;
}
case 7:
{
return 0;
}
}
}
}

Answer 1

Your problem is that the size of your array is 0. Here you set size to 0 and then size for the size of p1
int size=0;
int counter=0;
p1 = new int[size];
You are going to need to make size bigger so that you can actually store elements in p1 or instead of using arrays and dynamic memory allocation use a std::vector and let it handle that for you.

Answer 2

The code has undefined behaviour because initailly the dynamically allocated array pointed to by pointer p1 has no elements
int size=0;
^^^^^^^^^^
//...
p1 = new int[size]; // size is equal to 0
So in the following code snippet an atttempt to write data to p1[size] results in undefined behaviour
case 1: //Insert Number
cout<<"Enter a Number: ";
cin>>p1[size]; // undefined behaviour
^^^^^^^^^^^^^
counter++;
size++; //Add's memory space
break;
You need to reallocate the array to reserve memory for the added new element.
Take into account that for example this loop
for (i = 0; i>size; i++)
^^^^^^^
{
if (p1[size] == usearch)
break;
}
will never iterate because variable i set to zero can not be greater than size that at least equal to zero.
And it would be logically more correct to write
if (p1[i] == usearch)
^^^^^
instead of
if (p1[size] == usearch)
^^^^^^^^
Consequently this if statement
if (usearch == size)
^^^^^^^
{
cout << "not found. ";
}
should be replaced with this for statement
if (i == size)
^^
{
cout << "not found. ";
}