The Payroll Program
Loop Revisited

	cin >> empNum;
	moreData = (empNum != 0); // Initialize flag
	while (moreData)
	{
	.
	.
	.
	cin >> empNum; // Get the next
	// employee number
	moreData = (empNum != 0); // Update the flag
	// accordingly
	}

Looping Subtasks

	Counting
	Summing
	Keeping Track of a Previous Value

Counting

	count = 0; // Initialize counter
	cin.get(inChar); // Read the first character
	while (inChar != ‘.’)
	{
	count++; // Increment counter
	cin.get(inChar); // Get the next character
	}

Summing

	sum = 0;
	count = 1; // Initialize count
	while (count <= 10)
	{
	cin >> number; // Input a value
	sum = sum + number; // Add the value to
	count++;         // the sum
	}

Another Summing Example

	count = 0; // Initialize event counter
	sum = 0; // Initialize sum
	lessThanTen = true; // Initialize flag
	while (lessThanTen)
	{
	cin >> number; // Get the next value
	if (number % 2 == 1) // Is the value odd?
	{
	count++; // Yes – Increment counter
	sum = sum + number; // Add value to sum
	lessThanTen = (count < 10);  // Update flag
	}
	}

Recognizing Two
Character Sequences

	//***********************************************
	// NotEqualCount program
	// This program counts the occurrences of "!=" in a
	// data file
	//***********************************************
	#include <iostream>
	#include <fstream>   // For file I/O
	using namespace std;
	int main()
	{
	int      count;     // Number of != operators
	char     prevChar;     // Last character read

Recognizing Two
Character Sequences

	char     currChar;     // Character read in this loop
	// iteration
	ifstream inFile;        // Data file
	inFile.open("myfile.dat");   // Attempt to open
	// input file
	if ( !inFile )              // Was it opened?
	{
	cout << "** Can't open input file **"  // No—print
	// message
	<< endl;
	return 1;                         // Terminate
	// program
	}

More Recognizing Two
Character Sequences

	count = 0;             // Initialize counter
	inFile.get(prevChar);  // Initialize previous value
	inFile.get(currChar);  // Initialize current value
	while (inFile) // While previous input succeeded...
	{
	if (currChar == '=' &&  // Test for event
	prevChar == '!')
	count++;            // Increment counter
	prevChar = currChar;    // Replace previous value
	//   with current value
	inFile.get(currChar);   // Get next value
	}

Recognizing Two Character
Sequences (The End)

	cout << count << " != operators were found."
	<< endl;
	return 0;
	}

How to Design Loops

	Points to Consider
		What is the condition that ends the loop?
		How should the condition be initialized?
		How should the condition be updated?
		What is the process being repeated?
		How should the process be initialized?
		How should the process be updated?
		What is the state of the program on exiting the loop?

Is This a Well-Formed Loop?

	commaCount = 1;
	cin.get(inChar);
	while (inchar != ‘\n’)
	{
	if (inChar == ‘,’)
	commaCount++;
	cin.get(inChar);
	}
	cout << commaCount << endl;

Is This a Well-Formed Loop?
- No, So Fix It

	commaCount = 0;
	cin.get(inChar);
	while (inchar != ‘\n’)
	{
	if (inChar == ‘,’)
	commaCount++;
	cin.get(inChar);
	}
	cout << commaCount << endl;

Nested Logic

	cin.get(inChar); // Initialize outer loop
	while (cin) // Outer loop test
	{
	commaCount = 0; // Initialize inner loop
	// (Priming read for outer
	// loop also primes this one
	while (inChar != ‘\n’) // Inner loop test
	{
	if (inChar == ‘,’)
	commaCount++;
	cin.get(inChar);  // Update inner loop condition
	}
	cout << commaCount << endl;
	cin.get(inChar); // Update outer loop condition
	}

Another Nested Loop Example

	cin >> starCount;
	while (cin)
	{
	loopCount = 1;
	while (loopCount <= starCount)
	{
	cout << ‘*’;
	loopCount++;
	}
	cout << endl;
	cin >> starCount;
	}
	cout << “Goodbye” << endl;

Problem-Solving Case Study

	Problem: You are asked to compute the average salaries for male and female employees of a company.
	Input: A file, incFile (ifstream), of floating-point salary amounts (float), one per line, preceded by ‘F’ or ‘M’ (char).
	Output: All the input data. The number of females (int), average income (float). The number of males (int), average income (float)

Problem-Solving Case Study (Continued)

	Discussion: There are three main steps
		Process the data, counting and summing the salary amounts for each sex
		Compute the averages
		Print the calculated results
	Assumptions: There is at least one male and one female among all the data sets. The only gender codes in the file are ‘M’ and ‘F’ – any other codes are counted as ‘M’.

"//*****************************************************"

	//*****************************************************
	// Incomes program
	// This program reads a file of income amounts
	// classified by gender and computes the average
	// income for each gender
	//*****************************************************
	#include <iostream>
	#include <iomanip>    // For setprecision()
	#include <fstream>    // For file I/O
	#include <string>     // For string type
	using namespace std;

Problem Solving Implementation

	int main()
	{
	char     sex;       // Coded 'F' = female, 'M' = male
	int      femaleCount; // Number of female income amounts
	int      maleCount;   // Number of male income amounts
	float    amount;      // Amount of income for a person
	float    femaleSum;   // Total of female income amounts
	float    maleSum;     // Total of male income amounts
	float    femaleAverage;    // Average female income
	float    maleAverage;      // Average male income
	ifstream incFile;          // File of income amounts
	string     fileName;         // External name of file

Problem Solving Implementation

	cout << fixed << showpoint    // Set up floating pt.
	<< setprecision(2);     //   output format
	// Separately count females and males, and sum incomes
	// Initialize ending condition
	cout << "Name of the income data file: ";
	cin >> fileName;
	incFile.open(fileName.c_str());  // Open input file
	// and verify attempt
	if ( !incFile )
	{
	cout << "** Can't open input file **" << endl;
	return 1;
	}

"incFile >> sex >> amount"

	incFile >> sex >> amount;    // Perform priming read
	femaleCount = 0;             // Initialize process
	femaleSum = 0.0;
	maleCount = 0;
	maleSum = 0.0;
	while (incFile)
	{
	// Update process
	cout << "Sex: " << sex << " Amount: "
	<< amount << endl;

Problem Solving Implementation

	if (sex == 'F')
	{
	femaleCount++;
	femaleSum = femaleSum + amount;
	}
	else
	{
	maleCount++;
	maleSum = maleSum + amount;
	}
	// Update ending condition
	incFile >> sex >> amount;
	}

Problem Solving Implementation

	// Compute average incomes
	femaleAverage = femaleSum / float(femaleCount);
	maleAverage = maleSum / float(maleCount);
	// Output results
	cout << "For " << femaleCount << " females, "
	<< " the average income is " << femaleAverage
	<< endl;
	cout << "For " << maleCount << " males, the average "
	<< "income is " << maleAverage << endl;
	return 0;
	}

One More while Loop

	int main()
	{
	ifstream inFile;
	ofstream outFile;
	inFile.open(“prob4.in”);
	outFile.open(“prob4.out”);
	char ch;
	inFile.get(ch);
	while(inFile)
	{
	if (ch != ‘\t’)
	outFile.put(ch);
	infile.get(ch);
	}