An election is contested by five candidates. The candidates are numbered 1 to 5 and the voting is done by making the candidate number on the ballot paper. Write a program to read the ballots and count the votes cast for each candidate using an array variable count. In case, a number read is outside the range 1 to 5, the ballot should be considered as a 'spoilt ballot', and the program should also count the number of spoilt ballots.

 Here is a C++ program that reads the ballots and counts the votes cast for each candidate and the number of spoilt ballots:

#include <iostream>
using namespace std;

int main() {
   int count[5] = {0}; // initialize count array with 0s
   int spoilt_ballots = 0;
   int candidate;

   // read ballots until -1 is entered
   cout << "Enter the candidate number (1-5) on the ballot paper (-1 to stop):\n";
   cin >> candidate;
   while (candidate != -1) {
      if (candidate >= 1 && candidate <= 5) {
         count[candidate-1]++;
      } else {
         spoilt_ballots++;
      }
      cin >> candidate;
   }

   // display the results
   for (int i = 0; i < 5; i++) {
      cout << "Candidate " << i+1 << " received " << count[i] << " votes.\n";
   }
   cout << "There were " << spoilt_ballots << " spoilt ballots.\n";
   return 0;
}

Explanation:

1. We start by defining an integer array count of size 5 to keep track of the votes cast for each candidate. We also initialize all elements to 0 using the curly brace notation {0}.
2. We define an integer variable spoilt_ballots to keep track of the number of spoilt ballots. We initialize it to 0.
3. We define an integer variable candidate to read the candidate number from the user.
4. We use a while loop to read the ballots until the user enters -1 to stop.
5. Inside the loop, we check if the candidate number is between 1 and 5 (inclusive). If it is, we increment the count for that candidate by accessing the corresponding element in the count array. If it is not, we increment the spoilt_ballots counter.
6. After the loop ends, we use a for loop to display the results. For each candidate, we display their number and the number of votes they received by accessing the corresponding element in the count array. We also display the total number of spoilt ballots.
7. Finally, we return 0 to indicate successful program termination.