Notes

Outline

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); }