Problem selving and program design in C

Problem Solving Illustrated

In this section, we examine two programming problems that illustrate many of the

concepts discussed in this chapter. The top-down design process will be demonstrated

in solving each programming problem. Each program will be implemented

in a stepwise manner, starting with a list of major algorithm steps and continuing to

add detail through refinement until the program and its function subprogram can be

written. The first problem uses files and file pointers. The second problem implements

a set of functions for manipulating fractions.

PROBLEM

An architect needs a program that can estimate the appropriate size for the collecting

area of a solar-heated house. Determining collecting area size requires

consideration of several factors, including the average number of heating degree

days for the coldest month of a year (the product of the average difference between

inside and outside temperatures and the number of days in the month), the heating requirement per square foot of floor space, the floor space, and the efficiency of

the collection method. The program will have access to two data files. File hdd.txt

contains numbers representing the average heating degree days in the construction

location for each of 12 months. File solar.txt contains the average solar insolation

(rate in BTU/day at which solar radiation falls on one square foot of a given location)

for each month. The first entry in each file represents data for January, the second,

data for February, and so on.

ANALYSIS

The formula for approximating the desired collecting area ( A ) is

A _ heat loss

energy resource

In turn, heat loss is computed as the product of the heating requirement, the floor

space, and the heating degree days. We compute the necessary energy resource by

multiplying the efficiency of the collection method by the average solar insolation

per day and the number of days.

In all of our previous programs, data for program inputs have come from the

same source—either the keyboard or a file. In this program we will use three input

sources: the two data files and the keyboard. We can now identify the problem’s

data requirements and develop an algorithm.

DATA REQUIREMENTS

Problem Inputs

Average heating degree days file

Average solar insolation file

heat_deg_days /* average heating degree days for coldest month */

coldest_mon /* coldest month (number 1 .. 12) */

solar_insol /* average daily solar insolation (BTU/ft^2)for

coldest month */

heating_req /* BTU/degree day ft^2 for planned type construction*/

efficiency /* % of solar insolation converted to usable heat */

floor_space /* square feet */

Program Variables

energy_resrc /* usable solar energy available in coldest month

(BTUs obtained from 1 ft^2 of collecting area) */

Problem Outputs

heat_loss /* BTUs of heat lost by structure in coldest month */

collect_area /* approximate size (ft^2) of collecting area needed*/

DESIGN

Initial Algorithm

1. Determine the coldest month and the average heating degree days for this

month.

2. Find the average daily solar insolation per ft 2 for the coldest month.

3. Get from the user the other problem inputs: heating_req , efficiency , and

floor_space .

4. Estimate the collecting area needed.

5. Display results.

As shown in the structure chart ( Fig. 6.12 ), we will design step 2 as a separate

function. Function nth_item will find the value in file solar.txt that corresponds to

the coldest month. Steps 3 and 5 are quite straightforward, so only steps 1 and 4 call

for refinement here.