Why is my linear search always returning false, even if the item is in the array?

Question

I'm in an Intro to C++ class, and for one of our assignments we're making an online shop. One of our problems is to make a search function for the inventory, using a linear search, then display the corresponding price, stock, and shipability for that item.

For some reason, no matter how much I try and tweak it, it always returns false for the search, and that the store doesn't carry the item, even if I type in an item that I know is in the items array.

For example, if I type Moon Pie (which is in my array) in the getline, it'll still return as -1 like it isn't. Anything noticeably wrong with this code?

Here's my inputInventory.txt

Moon Pie    3.50    15  1
Cosmic Brownie  2.00    12  0
Moon Shine  7.00    7   1
Astronaut Icecream  4.00    11  1
Neptune Nuggets 2.50    30  1
Venus Vodka 6.50    10  1
Planet Pop  4.50    20  0
Starry Salad    3.00    15  0
Celeste Cakes   5.00    11  1
Plasma Potion   9.99    4   1
Star Fruit  2.50    10  1
Sun-dae 7.00    20  0
Moon Cheese 5.00    10  1
Milky Way Milkshake 6.50    5   0
Pluto Pie   7.00    9   10

#include <iostream>
#include <iomanip>
#include <fstream>
#include <string>
using namespace std;

const int MAX = 15;
void searchInventory(string itemNames[], double itemCost[], int itemNoShip[MAX][2]);
int linearSearch(string arr[], int size, string value);

int main() {
  int input;
  string items[MAX];
  double priceItems[MAX];
  int noItems[MAX][2];

  cout << "\n1. Read in Inventory\n";
  cout << "2. Display Inventory\n";
  cin >> input;

  while (input > 2 || input < 1) {
    cout << "An error has occured. Please input a value 1 - 2. >> ";
    cin >> input;
  }

  switch (input) {
    case 1:
      if (readInventory(items, priceItems, noItems) == true) {
        cout << "\nReading the file...\n";
      }
      break;
    case 2:
      searchInventory(items, priceItems, noItems);
      break;
  }
}

bool readInventory(string itemNames[], double itemCost[], int itemNoShip[MAX][2]) {
  bool fileRead = false;
  ifstream inputFile; // Pointer
  inputFile.open("inputInventory.txt");

  if (inputFile) // Test if file opened
  {
    for (int row = 0; row < MAX; row++) {
      getline(inputFile, itemNames[row], '\t');
      inputFile >> itemCost[row];
      inputFile >> itemNoShip[row][0];
      inputFile >> itemNoShip[row][1];
    }

    fileRead = true;
    inputFile.close();

  }
  return fileRead;
}

void searchInventory(string itemNames[], double itemCost[], int itemNoShip[MAX][2]) {
  string search;
  int result;
  int position;
  cout << "Please type the name of the item you are looking for. > ";
  cin.ignore();
  getline(cin,search);

  result = linearSearch(itemNames, MAX, search);

  cout << result;

  if (result >= 0) {
    cout << "\nYour item was found!\n";
    cout << itemNames[result] << itemCost[result] << itemNoShip[result][0] << "Shippable:" << itemNoShip[result][1];
  }
  else {
    cout << "\nThis item was not found in the list.";
  }
}

int linearSearch(string arr[], int size, string value) {
  int position;
  int index;
 
  for (index = 0; index < size; index++) {
    if (arr[index] == value) {
      position = index;
    } 
    else {
      position = -1;
    }
  }      
  
  return position;
}

Answer 1

The problem is cin.ignore(), since the default value of the first parameter is one, the first letter will always be taken out. So if someone typed "Moon Pie", the value in search will be "oon Pie".

Answer 2

for (index = 0; index < size; index++) 
        if (arr[index] == value) {
          position = index;
        } 
        else {
          position = -1;
        }
      

This loop continually overwrites position.

Unless your sought-after element is the last one in the array, immediately after it's been found the next element will cause position to be set to -1 again (unless that one matches too ).

You should stop looping (or, at least, stop updating position) as soon as a match is found.

Also, it would be advisable to wrap the entire loop body in {} braces, as that is conventional and what people will expect to see, making the code easier to read and to understand.

How about:

int linearSearch(string arr[], int size, string value)
{
    for (int index = 0; index < size; index++)
    {
        if (arr[index] == value)
            return index;
    }
    
    return -1;
}

Answer 3

You should break out of the for loop once you found the item, if not the loop will just continue and overwrite position. Edited: Based on PaulMcKenzie's comment, you should initialize position with a value so that it will not return garbage value.

int linearSearch(string arr[], int size, string value) {
  int position = -1;
  int index;
 
  for (index = 0; index < size; index++) {
        if (arr[index] == value) {
          position = index;
          break;
        }
  }
      
  return position;
}