Repetition

• Algorithms
• Uses : Counting and Sentinel controlled
• Pseudocode

 
Increment/Decrement revisited

• i = i + 1
• i += 1
• i++
• ++i

• Syntax

while (condition)
{
     statements_in_the_loop;
}
• Semantics
1. Evaluate the condition
2. If the condition is true

Execute the statements in the loop
Jump back to the top of the loop (step 1.)
3. Otherwise
        Execute statements after the loop
• EXAMPLES, Examples, examples

• Write a program that sums the numbers the user enters until a negative number is entered
• Write a program that calculates the average of three exam scores. If an exam score is below 0, keep asking for a correct number

• Syntax

do
{
     statements_in_the_loop;
} while (condition);
• Note the semicolon after the "(condition)"
• Semantics
1. Execute the statements in the loop
2. Evaluate the condition
3. If the condition is true

Jump back to the top of the loop (step 1.)
4. Otherwise
        Execute statements after the loop

1. sum two numbers
2. subtract two numbers
3. multiple two numbers
4. Quit

• Syntax for initial, final, and modifier

for (initialize_lcv; condition; modify_lcv)
{
     statements_in_loop;
}
statements_after_loop
• Semantics
1. Initialize lcv
2. Evaluate the condition
1. If the condition is true

Execute the statements in the loop
Jump back to the top of the loop (step 1.)
2. Otherwise
        Execute statements after the loop
• EXAMPLES

for (I=0; I<9; I++)
     cout << I;
 

• Write a program that sums the numbers from 1 until the number the user enters
• Write a program that displays the characters for the ASCII codes from 0 to 127

• Using loops to track a total
• Sentinel controlled loops
• Array preview
• Deciding which loop to use

Break

• Used to exit loop
• Caution when using
• Not "structured"
• Sometimes appropriate

Continue

• Used to skip to next iteration of loop
• Caution when using
• Not "structured"
• Rarely appropriate

Combining Control structures

• Programming using nested structures.

• Another way to get input into the program
• Pre-formatted text file
• Data not entered from keyboard
• Need to learn how to:
  1. Declare the file variable
  2. Open the filed and connect it to the actual file on disk
  3. Input (i.e., read) from a file
  4. Output to a file
  5. Close the file when you are done
• Need to include fstream
  #include <fstream>
• Declare an input file
  ifstream myFile;
• Declare an output file
  ofstream myReport;
• Open a file:
  myFile.open("theInput.txt");
  myReport.open("results.txt");
• Close a file
  myFile.close();
  myReport.close();
• Writing to a file uses the filename instead of cout
  myReport << "Report Title\n";
  myReport << "by Deborah Whitfield \n";
• Reading from a file uses the filename instead of cin
  myFile >> myNumericVariable;
  myFile >> myStringVariable;