หลักการโปรแกรม เพื่อแก้ปัญหาโดยใช้คอมพิวเตอร์ อ.จรรยา สายนุ้ย CS.313 ภาควิชาวิทยาการคอมพิวเตอร์

Outline Problem Solving Programming Principle Definition Strategies Techniques Tools Approach Programming Principle Programming Language Programming Design Programming Paradigms

Problem Solving Definition ................................................................................................................................ Problem Solving The process of transforming the description of a problem into the solution of that problem by using own knowledge of the problem domain and be relying on the ability to select and use appropriate problem solving strategies, techniques and tools

Problem Domain sciences : mathematics , statistics , chemistry , physics, biology business : inventory , accounting education : registration , evaluation banking : ATM , loaning , report others : restaurant , transportation , hotel , department store

Problem Solving Strategies (Algorithm Design Techniques) Divide and Conquer Dynamic Programming Greedy Algorithms etc.

Problem Solving Techniques Top-down Stepwise Refinement Structured Programming Modular Design Bottom-up Approach Recursion

Problem Solving Tools Pseudo Code Flowchart Programming Languages Editor Debugger

Problem Solving Approach Software Development Method or Software Life Cycle Use computers in problem solving consists of 6 steps : Requirement Specification Analysis Design Implementation Testing And Verification Documentation

Software Life Cycle Requirement Specification what the problem is what is needed to solve what the solution should provide any constraints and special conditions to concern depend on familiarity with the problem domain

Software Life Cycle Analysis Input Output Constraints/Conditions Formulas

Software Life Cycle Design 3.1 Algorithm design 3.2 Data design definition requirement strategy techniques 3.2 Data design Input/Output Process Types Representation Structure manipulation

Software Life Cycle Algorithm Definition 3.1 Algorithm design Algorithm : a method of solution described as a sequence of steps to be performed in a specific logical order.

Software Life Cycle Satisfied Requirements : 3.1 Algorithm design Unambiguousness Generality Correctness Finiteness

Software Life Cycle Representation Strategy 3.1 Algorithm design Pseudocoding Flowcharting HIPO Chart

Software Life Cycle 3.1 Algorithm design Greedy Method Techniques Greedy Method Divide and Conquer Dynamic Programming Backtracking Algorithms etc.

Software Life Cycle 3.2 Data design Input/Output Process Types : constant/variables ,global/local Representation: number , text , etc. Structure: array, file , queue , tree , etc. Manipulation: operators , functions ................................................................................................................................................................ ................................................................................................................................................ ......................................................................................................................................................................... .....................................................................................................................................................

Software Life Cycle Implementation or Coding Programming Languages writability readability modifiability reusability

Software Life Cycle Implementation or Coding Important as designing skill programming is the art of designing efficient algorithms to meet requirements Programming errors Debugging techniques Strategies for defensive Programming

Software Life Cycle Implementation or Coding Programming Errors design errors syntax/compilation errors linker errors run-time errors warning diagnostic message

Software Life Cycle Implementation or Coding Debugging techniques The ability to debug programs is another problem-solving skill that is as important as the ability to design programs Debugging is the process of finding and correcting errors in computer programs

Software Life Cycle Implementation or Coding Debugging techniques design errors quite difficult to debug , no error message , incorrect output sometimes incorrect formula , wrong program logic , inappropriate data type careful review in analysis and design , use variety of testing data

Software Life Cycle Implementation or Coding Debugging techniques syntax/compilation errors Detect by compilers Something missing / undeclared var. Easy , just correct error sources warning diagnostic message Strange but can still proceed Unreferenced var. Get rid of causes or ignore

Software Life Cycle Implementation or Coding Debugging techniques linker errors Some errors prevent the linker to create the executable module Function prototypes do not match their definitions solution: correct prototypes

Software Life Cycle Implementation or Coding Debugging techniques run-time/execution errors while executing , difficult to debug, abnormal termination divide by zero , type mismatch ,index is out of range, domain error trace/step watch some variables’ value , error handling

Software Life Cycle Strategies for defensive correction : errors debug Implementation or Coding Strategies for defensive correction : errors debug defence : to prevent abnormal termination /errors preparing to manage errors if (a < o) { … } using exception handler

Software Life Cycle Testing And Verification program verification the process of ensuring that a program meets user requirements one of the techniques that can be used for program verification is program testing

Software Life Cycle Testing And Verification program testing the process of executing a program to demonstrate its correctness testing methods test data testing modules : driver , stub top-down testing bottom-up testing blackbox .vs. whitebox

Software Life Cycle: Example Requirement Specification เขียนโปรแกรมหาระยะทางระหว่างจุด 2 จุดคือ (x1 ,y1 ) และ (x2 ,y2 ) สูตรคือ

Software Life Cycle : Example Analysis Input: integer x1 , y1 , x2 และ y2 Output : float & positive value Formulas :

Software Life Cycle: Example Algorithm Design Pseudocode Read x1 , y1 , x2 , y2 dist = sqrt((x1 - x2)2 + (y1 - y2)2) Write dist end

Software Life Cycle: Example Implementation or Coding #include <stdio.h> #include <math.h> void main() { int x1, x2, y1, y2; float dist; scanf(“%d %d %d %d”, &x1, &y1, &x2, &y2); dist = sqrt((x2-x1)*(x2-x1)+(y2-y1)*(y2-y1)); printf(“distance = %f\n”,dist); }

Software Life Cycle: Example Testing And Verification verifying: compile and debug data test: 3 0 0 4 output: 5.0

Software Life Cycle Documentation System documentation Program documentation User documentation

Software Life Cycle Documentation System documentation Context Diagram Dataflow Diagram Database Design : E-R diagram , Relational model , Data dictionary System modules/flowchart

Software Life Cycle Documentation Program documentation Flowchart / Pseudocode Program Listing Sufficient in-program : comment , indentation

Software Life Cycle Documentation User documentation Interfaces Input Examples Output Examples Error messages : causes & effect

Programming Principles Programming Languages Program Design Programming Paradigms

Programming Languages Why programming languages ? to enable the user to enlist the help of a computer in solving problems in the domain of interest to enable the user to bridge the gap between problem and machine domain

Program Design modular design stepwise refinement top-down approach bottom-up approach stepwise refinement structured programming etc.

Programming paradigms imperative paradigm functional paradigm logic paradigm object-oriented paradigm

Practice make perfect