Chapter 3 – Working with Batches of Data

#include <algorithm>
#include <iostream>
#include <vector>

using std::cin;
using std::cout;
using std::endl;
using std::sort;
using std::vector;

int main()
{
   // ask for and read the integers
   cout << "Please enter the integers that are to be "
      "arranged into quartiles, followed by end-of-file: ";

   vector<double> values;
   int x;

   // invariant: values contains all of the integers read so far
   while (cin >> x)
      values.push_back(x);

   typedef vector<double>::size_type vec_sz;
   vec_sz size = values.size();

   // check that the user entered more than one value, since a 
   // single value would cause an error
   if (size < 2)
   {
      cout << endl << "You must enter at least two values. " 
         "Please try again." << endl;
      return 1;
   }

   // sort the values
   sort(values.begin(), values.end());

   // find the median of the entire set of values
   vec_sz mid = size/2;
   double median;
   median = size % 2 == 0 ? (values[mid] + values[mid-1]) / 2
      : values[mid];

   // find the size of the lower and upper sets
   vec_sz half_size = size % 2 == 0 ? mid : (mid % 2 == 0 ? mid - 1 : mid);

   // find the midpoint of the lower and upper sets
   vec_sz half_mid = half_size / 2;

   // find the median of the lower set, which is the lower quartile
   double lower_quartile;
   lower_quartile = half_size % 2 == 0 ? (values[half_mid] + values[half_mid-1]) / 2
      : values[half_mid];

   // find the median of the upper set, which is the upper quartile
   vec_sz upper_mid = size % 2 == 0 ? half_size + half_mid : half_size + half_mid + 1;
   double upper_quartile;
   upper_quartile = half_size % 2 == 0 ? (values[upper_mid] + values[upper_mid-1]) / 2
      : values[upper_mid];

   cout << "The quartiles are " << lower_quartile << ", " 
      << median << ", and " << upper_quartile << endl;

   return 0;
}

Please enter the integers that are to be arranged into quartiles, followed by end-of-file: 11
43
7
24
89
10
^Z
The quartiles are 10, 17.5, and 43

#include <algorithm>
#include <iostream>
#include <string>
#include <vector>

using std::cin;
using std::cout;
using std::endl;
using std::sort;
using std::string;
using std::vector;

int main()
{
   // Ask for and read the words
   cout << "Please enter a few words, followed by end-of-file: ";

   vector<string> words;
   string word;

   // Invariant: words contains all of the words read so far
   while (cin >> word)
      words.push_back(word);

   typedef vector<string>::size_type vec_sz;
   vec_sz size = words.size();

   // Check that the user entered some words
   if (size == 0)
   {
      cout << endl << "You didn't enter any words. " 
         "Please try again." << endl;
      return 1;
   }

   // sort the words
   sort(words.begin(), words.end());

   string current_word;
   int count;

   // Set the initial word to the first word in the vector
   current_word = words[0];

   // Set the initial count for the first word
   count = 1;

   // Invariant: we have counted current_index of the total words 
   // in the vector
   for (vec_sz current_index = 1; current_index < size; ++current_index)
   {
      // Report the count for the current word if it does not match 
      // the word at the current index in the vector, and reset the 
      // count to zero so that it will one when the variable is 
      // incremented outside the if statement.
      if (current_word != words[current_index])
      {
         cout << "The word \"" << current_word << "\" appears " 
            << count << " times." << endl;

         current_word = words[current_index];
         count = 0;
      }

      ++count;
   }

   // Report the count for the final word
   cout << "The word \"" << current_word << "\" appears " 
      << count << " times." << endl;

   // We have reported the count of all the words in the vector, so exit.
   return 0;
}

Please enter a few words, followed by end-of-file: Na
na
na
na
hey
hey
goodbye
^Z
The word "Na" appears 1 times.
The word "goodbye" appears 1 times.
The word "hey" appears 2 times.
The word "na" appears 3 times.

#include <iostream>
#include <string>

using std::cin;
using std::cout;
using std::endl;
using std::string;

int main()
{
   // Ask for and read the words
   cout << "Please enter a few words, followed by end-of-file: ";

   string::size_type shortest_size = 0;
   string::size_type longest_size = 0;

   string word;

   while (cin >> word)
   {
      // If shortest_size is zero, it hasn't been assigned yet. 
      // Otherwise, see if the current word is shorter. If so, assign 
      // the current word's size to shortest_size.
      if (shortest_size == 0 
          || word.size() < shortest_size)
         shortest_size = word.size();

      // See if the current word is longer than longest_size. If so, 
      // assign the current word's size to longest_size.
      if (word.size() > longest_size)
         longest_size = word.size();
   }

   // Report the lengths of the shortest and longest words
   cout << "The length of the shortest word is " << shortest_size 
      << " and the length of the longest word is " << longest_size
      << endl;

   return 0;
}

Please enter a few words, followed by end-of-file: this
was
their
finest
hour
^Z
The length of the shortest word is 3 and the length of the longest word is 6

#include <iostream>
#include <string>
#include <vector>

using std::cin;
using std::cout;
using std::endl;
using std::string;
using std::vector;

int main()
{
   /* The number of grades accepted may be modified by changing this constant. */
   const int max_grades = 5;

   vector<string> student_names;
   vector<double> student_grades;

   cout << "Please enter the first student's name: ";
   string name;

   int grade;
   int grade_count;

   while (cin >> name)
   {
      cout << "Enter " << max_grades << " grades for " << name << ": ";

      student_names.push_back(name);
      grade_count = 0;

      while (grade_count < max_grades && cin >> grade)
      {
         student_grades.push_back(grade);
         ++grade_count;
      }

      cout << "Please enter the next student's name "
         "or end-of-file to exit: ";
   }

   cout << endl;
   cout << "** Grades and averages for each student **" << endl;

   typedef vector<string>::size_type name_vec_sz;
   name_vec_sz student_count = student_names.size();

   typedef vector<double>::size_type grade_vec_sz;
   grade_vec_sz grade_index = 0;

   double grade_total;

   /* For each student in student_names, retrieve max_grades values from 
   student_grades, output each grade, then calculate and output average. */
   for (name_vec_sz student_name_index = 0; 
        student_name_index < student_count; 
        ++student_name_index)
   {
      /* Reset the accumulator for each student */
      grade_total = 0;

      cout << "Student: " << student_names[student_name_index] << endl;
      cout << "Grades: ";

      /* Retrieve only max_grades grades from student_grades vector */
      for (grade_count = 0; grade_count < max_grades; ++grade_count)
      {
         cout << student_grades[grade_index] << " ";
         grade_total += student_grades[grade_index];
         ++grade_index;
      }

      cout << endl;
      cout << "Average: " << grade_total / max_grades << endl;
      cout << endl;
   }

   return 0;
}

Please enter the first student's name: Larry
Enter 5 grades for Larry: 89
88
78
98
85
Please enter the next student's name or end-of-file to exit: Moe
Enter 5 grades for Moe: 99
88
79
78
96
Please enter the next student's name or end-of-file to exit: Curly
Enter 5 grades for Curly: 99
98
99
97
100
Please enter the next student's name or end-of-file to exit: ^Z

** Grades and averages for each student **
Student: Larry
Grades: 89 88 78 98 85
Average: 87.6

Student: Moe
Grades: 99 88 79 78 96
Average: 88

Student: Curly
Grades: 99 98 99 97 100
Average: 98.6

Please enter your first name: Paul
Hello, Paul!
Please enter your midterm and final exam grades: ^Z
Enter all your homework grades, followed by end-of-file: Your final grade is -1.#J

#include <iomanip>
#include <ios>
#include <iostream>
#include <string>

using std::cin;
using std::cout;
using std::endl;
using std::setprecision;
using std::string;
using std::streamsize;

int main()
{
   // ask for and read the student's name
   cout << "Please enter your first name: ";
   string name;
   cin >> name;
   cout << "Hello, " << name << "!" << endl;

   // ask for and read the midterm and final grades
   cout << "Please enter your midterm and final exam grades: ";
   double midterm, final;
   cin >> midterm >> final;

   // ask for the homework grades
   cout << "Enter all your homework grades, "
      "followed by end-of-file: ";

   // the number and sum of grades read so far
   int count = 0;
   double sum = 0;

   // a variable into which to read
   double x;

   // invariant:
   //   we have read count grades so far, and
   //   sum is the sum of the first count grades
   while (cin >> x) {
      ++count;
      sum += x;
   }

   if (count == 0)
   {
      cout << endl << "No grades were entered. Your final grade cannot be calculated." << endl;
      return 1;
   }

   // write the result
   streamsize prec = cout.precision();
   cout << "Your final grade is " << setprecision(3) 
        << 0.2 * midterm + 0.4 * final + 0.4 * sum / count 
        << setprecision(prec) << endl;

   return 0;
}

Please enter your first name: Paul
Hello, Paul!
Please enter your midterm and final exam grades: ^Z
Enter all your homework grades, followed by end-of-file:
No grades were entered. Your final grade cannot be calculated.