CSCI 1110 - C++ Lecture Notes
Chapter 11 - One-Dimensional Arrays

Structured Data Types

One-Dimensional Arrays

Initializing Arrays in Delcarations

Aggregate Array Operations

Passing Arrays as Parameters

Case Study - Frequency of All Characters

Structured Data Types

• Simple data types consist of a single value. Examples of simple C++ data types are char, int, float, double, etc.
  
  
• A Structured Data Type is a collection of components whose organization is characterized by the method used to access individual components.
  
  
• The allowable operations on a structured data type include the storage and retrieval of individual components.
  
  

One-Dimensional Arrays

• If we wanted to read in a list of 1000 values and print them in reverse order, we could write a program of this form:
  
  

    // Reverse list program
    #include <iostream.h>
 
    int main()
    {
        int value0;
        int value1;
          . . .
        int value999;

        cin >> value0;
        cin >> value1;
          . . .
        cin >> value999;

        cout << value999;
        cout << value998;
          . . .
        cout << value0;
        return 0;
    }

This program is over 3000 lines long and contains 3000 variables which have the same name (value) with a numeric suffix. 


 

• A one-dimensional array provides a mechanism for keeping track of a number of values which share the same name. Individual items in the array can be referenced by an integeral value called an index.
  
  
• All members of an array must be of the same data type.
  
  
• To declare an array variable, specify the data type of members of the array, the name of the array, and the number of elements enclosed in square brackets:
  
  

    int value[1000];

This reserves memory for a 1000 element array of ints that is called value. 



• To reference individual members of an array, use the name of the array followed by the index of the element enclosed in square brackets. The index can be an integral constant, variable, or expression.
  
  

    cout << value[0]; // output first value
    value[999] = value[0];
    value[i] = value[j];
    value[i] = value[i - 1]; 



• Reverse program done with arrays:
  
  

    // Reverse list program
    #include <iostream.h>
 
    int main()
    {
        int value[1000];
        int number;

        for (number = 0; number < 1000; number++)
            cin >> value[i];

        for (number = 999; number >= 0; number--)
            cout << value[i];
 
        return 0;
    }
 



•  A one-dimensional array is a structured collection of components, all of the same type, that is given a single name. Each component (array element) is accessed by an integral index that indicates the component's position within the collection.
  
  
• C++ does not check to make sure that the index expression is valid. An out-of-bounds array index is either less than zero or greater than the array size minus one.




    float alpha[100];
    int i;

    for (i = 0; i < 100; i++)    // valid
        alpha[i] = 0.0;

    for (i = 0; i <= 99; i++)    // valid
        alpha[i] = 0.0;

    for (i = 0; i <= 100; i++)   // not valid
        alpha[i] = 0.0;

    for (i = 99; i >= 0; i--)    // not valid
        alpha[i] = alpha[i + 1];

Initializing Arrays in Delcarations

• To initialize the elements of an array when it is declared, follow the array declaration with the assignment operator followed by a list of data values seperated by commas and enclosed in braces:




    int age[5] = {23, 10, 45, 14, 92};
    char name[4] = {'T', 'o', 'm', '\0'};
    float temp[3] = {98.6, 1.4E2, -27.8};


• C++ will determine the size of a array automatically if you specify it initial values:
  
  
  
      int age[] = {23, 10, 45, 14, 92};

    char name[] = {'T', 'o', 'm', '\0'};
    float temp[] = {98.6, 1.4E2, -27.8};


• An array of characters can also be initialized by using a string of characters cnclosed in double quotes:
  
  
  
      char name[] = "Tom";
  
  
• Note that name contains four characters, including the '\0' character in position name[3].

Aggregate Array Operations

• An Aggregate Operation is an operation on a data structure as a whole, as opposed to an operation on an individual component of the data structure.
  
  
• Except for a few operations on arrays of characters (strings), which we will cover in Chapter 12, there aren't any aggregate array operations.
  
  
• To determine if two arrays are equal, you have to test all members of the arrays individually:
  
  
  
      int age[5] = {23, 10, 45, 14, 92};

    int year[5] = {23, 10, 45, 16, 92};
    bool equal = true;

    for (int i = 0; equal && i < 5; i++)
        equal = age[i] == year[i];




• Examples:
  
  
  
      // compute array sum as the sum of arrays
      // age and year
      int age[5] = {23, 10, 45, 14, 92};

    int year[5] = {23, 10, 45, 16, 92};
    int sum[5];

    for (int i = 0; i < 5; i++)
        sum[i] = age[i] + year[i];

    // -----------------------------------------

    // compute total as the sum of the members
    // of array temp
    float temp[3] = {98.6, 1.4E2, -27.8};
    float total = 0.0;

    for (i = 0; i < 3; i++)
        total += temp[i];

    // -----------------------------------------

    // output the number of meteors sighted
    // each night during an observation
    // and the total for the week
    enum Day {SUN, MON, TUE, WED, THU, FRI, SAT};
    int meteors[] = {4, 8, 43, 32, 17, 12, 8};
    int total = 0;

    for (Day i = SUN; i <= SAT; i = Day(i + 1))
    {
        cout << "Meteors during ";
        switch (i)
        {
            case SUN : cout << "Sunday";
                       break;
            case MON : cout << "Monday";
                       break;
            case TUE : cout << "Tuesday";
                       break;
            case WED : cout << "Wednesday";
                       break;
            case THU : cout << "Thursday";
                       break;
            case FRI : cout << "Friday";
                       break;
            case SAT : cout << "Saturday";
                       break;
        }
        cout << "'s observation was "
             << meteors[i] << "." << endl;
        total += meteors[i];
    }
    cout << "Total for the week was "
         << total << "." << endl;
 

Passing Arrays as Parameters

• By default, arrays are always passed to functions by reference, not by value.
  
  
• When any variable is passed to a function by reference, C++ actually sends the address of the variable to the function. The address that is passed to the function for arrays is the base address of the array.
  
  
• The Base Address of and array is the memory address of the first element of the array.
  
  
• Example of a function with an array parameter:
  
  
  
      void ZeroArray(float arr[], int nElements)
      {

        for (int i = 0; i < nElements; i++)
            arr[i] = 0.0;
    }



• Note that in the function heading, the size of the array arr is not specified. However, the number of elements in the array is passed to the function as a value parameter. This allows the function to be used with arrays of any size:

 


    float velocity[30];
    float warp[9000];

    . . .
 
    ZeroArray(velocity, 30);
    ZeroArray(warp, 9000);


• One of the reasons for using value parameters is that it prevents a function from changing the value of the variable. Since arrays are always passed by reference, C++ has another way to ensure that a function cannot change the values of the array:
  
  
  
      void CopyArray(const int source[],
                           int destination[],
                           int size)
      {

        for (int i = 0; i < size; i++)
            destination[i] = source[i];
    }

When the C++ reserved word const is used with a prarmeter, the function cannot alter that parameter.
 

Case Study - Frequency of All Characters

• On pages 629-635 of the text, there is a case study for a program that reads a text data file and produces a frequency count for all the printable characters in that file. 
  
  
• The design of the program is discussed in the text.
  
  
• The program can be viewed at CountAll program.