Topics covered on Monday, 2010-08-16

Summary

• Looping constructs: while and for
• Increment operator: ++
• Conditional operator: condition ? expression1 : expression2

Compute Average Program, version 1

     1  // average1.cpp
     2  //
     3  // Get numbers (after prompting for how many) and print average.
     4  // Use while loops and simple if test for formatting output.
     5  //
     6  // Copyright 2010, Raj Mathur
     7  //
     8  #include <iostream>
     9  #include <cstdlib>
    10  using namespace std;
    11
    12  int main(int argc, char *argv[])
    13  {
    14    int
    15      count = 0;
    16    float
    17      sum = 0;
    18    float
    19      average;
    20    // Get count
    21    cout << "How many numbers do you want the average for? ";
    22    cin >> count;
    23    // Allocate space
    24    int
    25      numbers[count];
    26    // Read the numbers
    27    int
    28      i = 0;
    29    while( i < count )
    30    {
    31      cout << "Next number: ";
    32      cin >> numbers[i];
    33      sum += numbers[i];
    34      i++;
    35    }
    36    // Compute average
    37    average = sum / count;
    38    // Format and print
    39    cout << "The average of (";
    40    i = 0;
    41    while( i < count )
    42    {
    43      if( i != 0 )
    44      {
    45        cout << ", ";
    46      }
    47      cout << numbers[i++];
    48    }
    49    cout << ") is ";
    50    cout << average << endl;
    51    exit(0);
    52  }

Computer Average Program, version 2

     1  // average2.cpp
     2  //
     3  // Get numbers (after prompting for how many) and print average.
     4  // Use for loops and conditional operator.
     5  //
     6  // Copyright 2010, Raj Mathur
     7  //
     8  #include <iostream>
     9  #include <cstdlib>
    10  using namespace std;
    11
    12  int main(int argc, char *argv[])
    13  {
    14    int
    15      count = 0;
    16    int
    17      i;
    18    float
    19      sum = 0;
    20    float
    21      average;
    22    // Get count
    23    cout << "How many numbers do you want the average for? ";
    24    cin >> count;
    25    // Allocate space
    26    int
    27      numbers[count];
    28    // Read the numbers
    29    for( i = 0; i < count; i++ )
    30    {
    31      cout << "Next number: ";
    32      cin >> numbers[i];
    33      sum += numbers[i];
    34    }
    35    // Compute average
    36    average = sum / count;
    37    // Format and print
    38    cout << "The average of (";
    39    for( i = 0; i < count; i++ )
    40    {
    41      cout << (i != 0 ? ", " : "") << numbers[i];
    42    }
    43    cout << ") is ";
    44    cout << average << endl;
    45    exit(0);
    46  }

Computer Average Program, version 3

     1  // average3.cpp
     2  //
     3  // Get numbers (after prompting for how many) and print average.
     4  // Use for loops and tricks to print appropriate separator without the
     5  // use of conditions
     6  //
     7  // Copyright 2010, Raj Mathur
     8  //
     9  #include <iostream>
    10  #include <cstdlib>
    11  using namespace std;
    12
    13  int main(int argc, char *argv[])
    14  {
    15    int
    16      count = 0;
    17    int
    18      i;
    19    float
    20      sum = 0;
    21    float
    22      average;
    23    // Get count
    24    cout << "How many numbers do you want the average for? ";
    25    cin >> count;
    26    // Allocate space
    27    int
    28      numbers[count];
    29    // Read the numbers
    30    for( i = 0; i < count; i++ )
    31    {
    32      cout << "Next number: ";
    33      cin >> numbers[i];
    34      sum += numbers[i];
    35    }
    36    // Compute average
    37    average = sum / count;
    38    // Format and print
    39    cout << "The average of (";
    40    const char
    41      *prefix = "";
    42    for( i = 0; i < count; i++ )
    43    {
    44      cout << prefix << numbers[i];
    45      prefix = ", ";
    46    }
    47    cout << ") is ";
    48    cout << average << endl;
    49    exit(0);
    50  }

Assignments

Review

Read and solve the attached PDF. Please put your solutions in a single text file and mail it to me as an attachment.

• assn1.pdf: Assignment 1 for Monday, 2010-08-16

Program

Modify your calculator program to do the following:

1. Handle (a)ddition, (s)ubtraction, mul(t)iplication and (d)ivision.
2. Handle invalid inputs.
3. Run in a loop and ask the user if she wants to do another operation before exiting.

A sample run of the program would now look exactly like this. Entries in bold are what the user enters, and formatting is important:

Do you want to (a)dd, (s)ubtract, mul(t)iply or (d)ivide? q
Sorry, I don't understand the 'q' operation. Try again.
Do you want to (a)dd, (s)ubtract, mul(t)iply or (d)ivide? t
Please enter the first number: 3
Please enter the second number: 5
The result is: 5

That was fun! Would you like to do another computation (y/n)? y
Do you want to (a)dd, (s)ubtract, mul(t)iply or (d)ivide? s
Please enter the first number: 23
Please enter the second number: 42
The result is: -19

That was fun! Would you like to do another computation (y/n)? n
Until later then. Bye!