Notes

Outline

File Input and Output A file is a named area in secondary storage that holds a collection of information (on disk, for example) Using files requires us to Request the preprocessor to include the header file fstream Use declaration statements to declare the file streams we are going to use Prepare each file for reading or writing by using a function named open Specify the name of the file stream in each input or output statement

Using Files All of the cin and cout operations work for files. Declaring File Streams ifstream inFile; ofstream outFile;        (With these data types, you cannot read from and write to the same file) Opening Files inFile.open(“cone.dat”); outFile.open(“results.dat”);   (Open associates a stream variable used in your program with a physical file on disk.) Specifying File Streams in Input/Output Statements inData >> htInInches >> diamInInches >> redPrice        >> bluePrice >> greenPrice; outData << “The painting cost for” << endl;

An Example Program Using Files //************************************************************ // ConePaint program // This program computes the cost of painting traffic cones in // each of three different colors, given the height and diameter // of a cone in inches, and the cost per square foot of each of // the paints, all of which are input from a file //************************************************************ #include <iostream> #include <iomanip>    // For setw() and setprecision() #include <cmath>      // For sqrt() #include <fstream>    // For file I/O using namespace std; const float INCHES_PER_FT = 12.0;   // Inches in 1 foot const float PI = 3.14159265;        // Ratio of circumference                                     //   to diameter

An Example Program Using Files int main() {     float    htInInches;    // Height of the cone in inches     float    diamInInches;  // Diameter of base of cone in inches     float    redPrice;      // Price per square foot of red paint     float    bluePrice;     // Price per square foot of blue paint     float    greenPrice;    // Price per square foot of green paint     float    heightInFt;    // Height of the cone in feet     float    diamInFt;      // Diameter of the cone in feet     float    radius;        // Radius of the cone in feet     float    surfaceArea;   // Surface area in square feet     float    redCost;       // Cost to paint a cone red     float    blueCost;      // Cost to paint a cone blue     float    greenCost;     // Cost to paint a cone green     ifstream inData;        // Holds cone size and paint prices     ofstream outData;       // Holds paint costs

An Example Program  Using Files outData << fixed << showpoint;         // Set up floating-pt.                                            //   output format     // Open the files     inData.open("cone.dat");     outData.open("results.dat");     // Get data     inData >> htInInches >> diamInInches >> redPrice            >> bluePrice >> greenPrice;     // Convert dimensions to feet     heightInFt = htInInches / INCHES_PER_FT;     diamInFt = diamInInches / INCHES_PER_FT;     radius = diamInFt / 2.0;

An Example Program Using Files // Compute surface area of the cone     surfaceArea = PI * radius *                   sqrt(radius*radius + heightInFt*heightInFt);     // Compute cost for each color     redCost = surfaceArea * redPrice;     blueCost = surfaceArea * bluePrice;     greenCost = surfaceArea * greenPrice;

An Example Program Using Files // Output results     outData << setprecision(3);     outData << "The surface area is " << surfaceArea << " sq. ft."             << endl;     outData << "The painting cost for" << endl;     outData << "   red is" << setw(8) << redCost << " dollars"             << endl;     outData << "   blue is" << setw(7) << blueCost << " dollars"             << endl;     outData << "   green is" << setw(6) << greenCost << " dollars"             << endl;     return 0; }

Run-Time Input of File Names inFile.open(“datafile.dat”) restricts us, we can’t run that program on another file, we’d like to make the file name an input to the program To do so, we need code like the following: ifstream inFile; string fileName; cout << “Enter the input file name: ”; cin >> filename; inFile.open(fileName.c_str());

Input Failure (How Things Can Go Very Wrong) If an input operation fails because of invalid data, the cin stream enters the silent but deadly fail state. (No error) Example: int i = 10, j = 20, k = 30; cin >> i >> j >> k; cout << i: ” << i << “  j: ” << j      << “  k: ” << k; Input Data 1234.56 7 89 produces this output: i: 1234  j: 20  k: 30

Software Design Methodologies Object-Oriented Design A technique for developing software in which the solution is expressed in terms of self-contained entities composed of data and operations on that data (objects). Functional Decomposition A technique for developing software in which the problem is divided into more easily handled subproblems, the solution of which creates a solution to the overall problem.

Software Design Methodologies Object-Oriented Design A technique for developing software in which the solution is expressed in terms of self-contained entities composed of data and operations on that data (objects). Functional Decomposition A technique for developing software in which the problem is divided into more easily handled subproblems, the solution of which creates a solution to the overall problem.

What are Objects? An object is a collection of data together with associated operations. In object-oriented programming languages, a class is a programmer-defined data type from which objects are created. iostream defines the classes istream and ostream and declares cin and cout istream cin; istream cout; string is also a class.

Functional Decomposition Functional decomposition is also known as structured design, top-down design, stepwise refinement and modular programming. By subdividing the problem, you create a hierarchical structure called a tree structure. Each level of the tree is more concrete than the level above it.

Hierarchical Structure Tree

Modules A module begins life as an abstract step in the next-higher level of the solution tree. It is completed when it solves a subproblem. Writing Cohesive Modules Think Begin writing major steps If a step is simple enough, stop If you have to break a step up, it’s still abstract If you have something hopelessly complicated, go back up a level

Functional Decomposition Example

Main Module Define constants Convert dimensions to feet Set radius = diamInFt/2 Compute surface area Compute costs Print results

Define Constants HT_IN_INCHES = 30.0 DIAM_IN_INCHES = 8.0 INCHES_PER_FT = 12.0 RED_PRICE = 0.10 BLUE_PRICE = 0.15 GREEN_PRICE = 0.18 PI = 3.14159265

"Convert dimensions to Feet" Convert dimensions to Feet Set heightInFt = HT_IN_INCHES/INCHES_PER_FT set diamInFt = DIAM_IN_INCHES/INCHES_PER_FT Compute Surface Area Set surfaceArea = pi x radius xsqrt(radius2 + heightInFt2)

Print Results Print surfaceArea Print redCost Print blueCost Print green Cost

Problem-Solving Case Study Problem: For your art class, you need to know how much wood to buy for a frame, how large a piece of canvas to purchase, and the cost of the materials for a given for a given painting size. Inputs: length and width of the painting (float), the cost per inch of wood (float), and the cost per square foot of canvas (float). Outputs: Prompting messages, the input data, length of wood to buy (float), the dimensions of the canvas (float), the cost of the wood (float), the cost of the canvas (float), and the total cost of the materials (float).

Problem-Solving Case Study (continued) Discussion: The length of the wood is twice the sum of the length and the width of the painting. The cost of the wood is simply its length times its cost per inch. For the canvas, we must add 5 inches to the length and width to allow for wrapping the canvas around the frame.The area is length times width, converted from square inches to square feet. Assumptions: The input values are positive (checking for erroneous data is not done).

Main Module Get length and width Get wood and canvas costs Compute dimensions and costs Print dimensions and costs

Get Length and Width Print “Enter length and width of painting” Read length, width

Get Wood  and Canvas Costs Print “Enter cost per inch of the framing wood in dollars” Read woodCost Print “Enter cost per square foot of canvas in dollars” Read canvasCost

Compute Dimensions and Costs Set lengthOfWood = (length + width) * 2 Set canvasWidth = width + 5 Set canvasLength = length + 5 Set canvasAreaInches = canvasWidth * canvasLength Set canvasAreaFeet = canvasAreaInches/144.0 Set totWoodCost = lengthOfWood * woodCost Set totCanvasCost = canvasAreaFeet * canvasCost Set totCost = totWoodCost + totCanvasCost

Print Dimensions and Costs Print “For a painting”, length, “in. long and”, width Print “in. wide, you need to buy”, lengthOfWood, “in.” Print “of wood and the canvas must be”, canvasLength Print “in. long and”, canvasWidth, “in. wide. Given a” Print “wood cost of $”, woodCost, “per in. and a” Print “canvas cost of $”, canvasCost, “per sq. ft., the” Print “wood will cost $”, totWoodCost, “, the canvas” Print “will cost $”, totCanvasCost, “, and the total cost” Print “of materials will be $”’, totCost, ‘.’

Module Structure Chart

Program Implementation So far, we’ve seen flat implementations, the hierarchical solution gets translated into a sequence of steps in one function. The alternative to flat implementations are hierarchical implementations with separate functions and call to those functions.