When the increment operator is used as in num1 ++ The expression is in this mode?

int main()
{
   const int MIN_NUMBER = 1,   // Starting value
             MAX_NUMBER = 10;  // Ending value
   int num;

   cout << "Number Number Squared\n";
   cout << "-------------------------\n";

   for (num = MIN_NUMBER; num <= MAX_NUMBER; num++)
      cout << num << "\t\t" << (num * num) << endl;

   return 0;
}

In any situation that clearly requires

–an initialization

–a false condition to stop the loop

–an update to occur at the end of each iteration

• The for loop tests its test expression before each iteration, so it is a pretest loop.
• The following loop will never iterate:
  

for (count = 11; count <= 10; count++)
   cout << "Hello" << endl;

for Loop - Modifications

You can have multiple statements in the initialization expression. Separate the statements with a comma:

int x, y;

for (x=1, y=1; x <= 5; x++)

{

cout << x << " plus " << y
        << " equals " << (x+y)
        << endl;

}

•           You can also have multiple statements in the test expression. Separate the statements with a comma:

int x, y;

for (x=1, y=1; x <= 5; x++, y++)
{
   cout << x << " plus " << y
        << " equals " << (x+y)
        << endl;
}

•          You can omit the initialization expression if it has already been done:

  int sum = 0, num = 1;

  for (; num <= 10; num++)

  sum += num;

•          You can declare variables in the initialization expression:

  int sum = 0;

  for (int num = 0; num <= 10; num++)

  sum += num;

  The scope of the variable num is the for loop.

5.7  Keeping a Running Total

• running total: accumulated sum of numbers from each repetition of loop
• accumulator: variable that holds running total

int sum=0, num=1; // sum is the

while (num <= 10) // accumulator

{    sum += num;

   num++;

}

cout << "Sum of numbers 1 – 10 is"

     << sum << endl;

A Running Total in Program 5-12

// This program takes daily sales figures over a period of time
// and calculates their total.
#include
#include
using namespace std;

int main()
{
   int days;            // Number of days
   double total = 0.0;  // Accumulator, initialized with 0

   // Get the number of days.
   cout << "For how many days do you have sales figures? ";
   cin >> days;

      // Get the sales for each day and accumulate a total.
   for (int count = 1; count <= days; count++)
   {
      double sales;
      cout << "Enter the sales for day " << count << ": ";
      cin >> sales;
      total += sales;   // Accumulate the running total.
   }

      // Display the total sales.
   cout << fixed << showpoint << setprecision(2);
   cout << "The total sales are $" << total << endl;
   return 0;
}

5.8  Sentinels

• sentinel: value in a list of values that indicates end of data
• Special value that cannot be confused with a valid value, e.g., -999 for a test score
• Used to terminate input when user may not know how many values will be entered

A Sentinel in Program 5-13

// This program calculates the total number of points a
// soccer team has earned over a series of games. The user
// enters a series of point values, then -1 when finished.
#include
using namespace std;

int main()
{
   int game = 1,   // Game counter
       points,     // To hold a number of points
       total = 0;  // Accumulator

   cout << "Enter the number of points your team has earned\n";
   cout << "so far in the season, then enter -1 when finished.\n\n";
   cout << "Enter the points for game " << game << ": ";
   cin >> points;

   while (points != -1)
   { 
      total += points;
      game++;
      cout << "Enter the points for game " << game << ": ";
      cin >> points;
   }
   cout << "\nThe total points are " << total << endl;
   return 0;
}

5.9  Deciding Which Loop to Use

•          The while loop is a conditional pretest loop
•         Iterates as long as a certain condition exits
•         Validating input 
•         Reading lists of data terminated by a sentinel
•          The do-while loop is a conditional posttest loop
•          Always iterates at least once
•          Repeating a menu
•          The for loop is a pretest loop
•         Built-in expressions for initializing, testing, and updating
•         Situations where the exact number of iterations is known

5.10  Nested Loops

• A nested loop is a loop inside the body of another loop
• Inner (inside), outer (outside) loops:

for (row=1; row<=3; row++)  //outer
    for (col=1; col<=3; col++)//inner
        cout << row * col << endl;

Nested for Loop in Program 5-14

// This program averages test scores. It asks the user for the
// number of students and the number of test scores per student.
#include
#include
using namespace std;

int main()
{
   int numStudents,  // Number of students
       numTests;     // Number of tests per student
   double total,     // Accumulator for total scores
          average;   // Average test score

   // Set up numeric output formatting.
   cout << fixed << showpoint << setprecision(1);

   // Get the number of students.
   cout << "This program averages test scores.\n";
   cout << "For how many students do you have scores? ";
   cin >> numStudents;

      // Get the number of test scores per student.
   cout << "How many test scores does each student have? ";
   cin >> numTests;

      // Determine each student's average score.
   for (int student = 1; student <= numStudents; student++)
   {
      total = 0;      // Initialize the accumulator.
      for (int test = 1; test <= numTests; test++)
      {
         double score;
         cout << "Enter score " << test << " for ";
         cout << "student " << student << ": ";
         cin >> score;
         total += score;
      }
      average = total / numTests;
      cout << "The average score for student " << student;
      cout << " is " << average << ".\n\n";
   }
   return 0;
}

Nested Loops - Notes

• Inner loop goes through all repetitions for each repetition of outer loop
• Inner loop repetitions complete sooner than outer loop
• Total number of repetitions for inner loop is product of number of repetitions of the two loops. 

5.11  Using Files for Data Storage

• Can use files instead of keyboard, monitor screen for program input, output
• Allows data to be retained between program runs
• Steps:
• Open the file
• Use the file (read from, write to, or both)
• Close the file

Files: What is Needed

• Use fstream header file for file access
• File stream types:

ifstream for input from a file
ofstream for output to a file
fstream for input from or output to a file

• Define file stream objects:

ifstream infile;
ofstream outfile;

Opening Files

• Create a link between file name (outside the program) and file stream object (inside the program)
• Use the open member function:

infile.open("inventory.dat");
outfile.open("report.txt");

• Filename may include drive, path info.
• Output file will be created if necessary; existing file will be erased first
• Input file must exist for open to work

Testing for File Open Errors

•          Can test a file stream object to detect if an open operation failed:

  infile.open("test.txt");

  if (!infile)

  {

   cout << "File open failure!";

  }

•          Can also use the fail member function

Using Files

•          Can use output file object and << to send data to a file:

  outfile << "Inventory report";

•          Can use input file object and >> to copy data from file to variables:

  infile >> partNum;

  infile >> qtyInStock >> qtyOnOrder;

Using Loops to Process Files

• The stream extraction operator >> returns true when a value was successfully read, false otherwise
• Can be tested in a while loop to continue execution as long as values are read from the file:

  while (inputFile >> number) ...

•          Use the close member function:

infile.close();

outfile.close();

•         Don’t wait for operating system to close files at program end:

–may be limit on number of open files

–may be buffered output data waiting to send to file

Letting the User Specify a Filename

• The open member function requires that you pass the name of the file as a null-terminated string, which is also known as a C-string.
• String literals are stored in memory as null-terminated C-strings, but string objects are not.
• string objects have a member function named c_str

–It returns the contents of the object formatted as a null-terminated C-string.

–Here is the general format of how you call the c_str function:

                    stringObject.c_str()

Letting the User Specify a Filename in Program 5-24

// This program lets the user enter a filename.
#include
#include
#include
using namespace std;

int main()
{
   ifstream inputFile;
   string filename;
   int number;

   // Get the filename from the user.
   cout << "Enter the filename: ";
   cin >> filename;

   // Open the file.
   inputFile.open(filename.c_str());

   // If the file successfully opened, process it.
   if (inputFile)
   {
      // Read the numbers from the file and
      // display them.
      while (inputFile >> number)
      {
         cout << number << endl;
      }

      // Close the file.
      inputFile.close();
   }
   else
   {
       // Display an error message.
       cout << "Error opening the file.\n";
   }
   return 0;
}

5.12 Breaking and Continuing a Loop

• Can use break to terminate execution of a loop
• Use sparingly if at all – makes code harder to understand and debug
• When used in an inner loop, terminates that loop only and goes back to outer loop

The continue Statement

• Can use continue to go to end of loop and prepare for next repetition
• while, do-while loops: go to test, repeat loop if test passes
• for loop: perform update step, then test, then repeat loop if test passes
• Use sparingly – like break, can make program logic hard to follow

What is the operator used for increment?

What does it mean to increment something what operator is used in C++ to do this?

What does ++ i mean in programming?

Which operator is used to increment a variable?