Passing Arrays To/From Functions

Array Parameters

• pass an array is the same as passing a pointer

• only the first part (pointer part) is passed, data part stays

• use [] syntax or * syntax

  // ==== Array parameter ====
  // ---- Correct ----
  
  // ignore the size
  double average(double arr[], int size);
  double average(double *arr, int size);
  
  // ---- Wrong ----
  double average(double arr[size], int size);  // not compile
  double average(double arr[3], int size);  // compile but 3 is ignored
  
  // ---- to call ----
  double arr1[3] = {1.0, 2.0, 3.0};
  cout << average(arr1, 3) << endl;
  // cout << average(arr1[], 3) << endl;  // wrong!
  

Return an Array

• Returning an array is the same as returning a pointer

• Only the first part (pointer part) is passed to outside, data part stays

• The return type should use pointer syntax

• Never return a local array from a function

  // ==== Array as returned value ====
  
  // ---- Correct ----
  // return a dynamic array
  int *makeSequence(int size) {
    int *sequence;
    sequence = new int[size];
    for (int i = 0; i < size; ++i)
      sequence[i] = i + 1;
    return sequence;
  }
  
  // ---- Wrong ----
  int *makeSequence(int size) {
    int sequence[size];
    for (int i = 0; i < size; ++i)
      sequence[i] = i + 1;
    return sequence;
  }
  
  // ---- to call ----
  int *seq = makeSequence(10);
  delete [] seq;
  

• Read the returning multidimensional arrays document as needed