23D. Example

The following program reads a list of integers from the standard input until it sees integer 0. Then it writes them to the standard output backwards. It is a silly program, but it illustrates use of arrays.

  #include <cstdio>
  using namespace std;

  const int maxNums = 100;

  // ReadNumbers(A) reads integers from the standard input
  // until it reads 0.  It stores the first value read
  // into A[0], the second value into A[1], etc.
  // It does not store the end marker 0 into array A.
  //
  // Array A is assumed to have physical size maxNums.
  //
  // ReadNumbers returns the number of values that it read,
  // excluding the 0 at the end.

  int readNumbers(int A[])
  {
    int i;

    for(i = 0; i < maxNums; i++)
    {
      scanf("%i", &(A[i]));
      if(A[i] == 0) 
      {
        break;
      }
    }
    return i;
  }

  // WriteNumbers(A, howmany) writes A[howmany-1], ...,
  // A[0], in that order, each on a separate line, to
  // the standard output.

  void writeNumbers(const int A[], const int howmany)
  {
    for(i = howmany - 1; i >= 0; i--)
    {
      printf("%i\n", A[i]);
    }

  }

  int main()
  {
    int howmany;
    int A[maxNums];

    howmany = readNumbers(A);
    writeNumbers(A, howmany);
    
    return 0;
  }  

Exercises

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1. An array is not always the right tool. Show how to simplify the above program substantially by using recursion. Answer