Cs1001 Lecture 2 Programming and problem solving

CS1001 Lecture 2

• Programming and problem solving

• Software engineering practices

Introduction

• Use computers as a problem solving tool

• A computer program is a sequence of instructions that must be followed to solve a particular problem.

• Software engineering is the study and application of programming and problem solving techniques and methodologies

Simple Program Design Process

Problem Statement

• A nuclear physicist is conducting research with the radioactive element polonium. The half-life of polonium is 140 days, which means that because radioactive decay, the amount of polonium that remains after 140 days is one-half of the original amount. How much polonium will remain after 180 days if 10 milligrams are present initially.

• What information is given? … which ones are important ?

• What information must be produced?

Data analysis and organization

• Specific

• Input Output

• Initial amount: 10 mg Amount remaining

• Half-life: 140 days

• Time period: 180 days

• Generalize

• Input Output

• Initial amount Amount remaining

• Half-life

• Time period

Algorithm Design & Refinement

• Get values for InitialAmount, HalfLife, and Time

• Compute the value of AmountRemaining for a given Time

• Display AmountRemaining

• AmountRemaining = InitialAmount*(0.5)**(Time/HalfLife)

Coding

• General form of Fortran program:

• Heading
• specification
• execution
• subprogram
• END PROGRAM

• Documentation

• Opening documentation
• http://www.cs.wpi.edu/Help/documentation-standard.html

Coding

• PROGRAM Radioactive_Decay

• !--------------------------------------------------------

• ! This program calculates the amount of a radioactive

• ! substance that remains after a specified time, given

• ! an initial amount and its half-life. Variables used are:

• ! InitalAmount : initial amount of substance (mg)

• ! HalfLife : half-life of substance (days)

• ! Time : time at which the amount remaining

• ! is calculated (days)

• ! AmountRemaining : amount of substance remaining (mg)

• !

• ! Input: InitialAmount, HalfLife, Time

• ! Output: AmountRemaining

• !---------------------------------------------------------

Preparing a Program for Execution

Testing

• Initial test -- the ones that you can calculate easily by hand. E.g.:

• InitialAmount = 2, HalfLife=140, Time=140. AmountRemaining should = 1.0000000 mg
• InitialAmount = 4, HalfLife=140, Time=280. AmountRemaining should = 1.0000000 mg.
• Then InitialAmount = 10, HalfLife=140, Time=180. AmountRemaining= 4.1016769 mg

• “Once we are confident that the program is correct”

• what? when? how? how much?

More Realistic Process

A typical testing process for a large program

Program Design Tips

• This process is often iterative because you may not initially know what all you want to print out, or input.

• Design a little
• Code a little
• Test a little
• Take a break
• Repeat until finished

Summary

• Program solving process, SE process

• Fortran statements:

• PROGRAM program_name
• IMPLICIT NONE
• REAL:: list_of_real_variables
• INTEGER:: list_of_integer_variables
• Comments !
• Continuation &
• Operations + - * / **
• Assignment =
• Input READ*, input_list_of_variables
• Output PRINT *, output_list_of variables
• END PROGRAM program_name