Programming Fundamentals 750113 Ch 1 Problem Solving Programming

Programming Fundamentals (750113) Ch 1. Problem Solving Programming Fundamentals --> Ch 1. Problem solving 1

Problem Solving • Programming is a process of problem solving (Problem Solution by computer) • Algorithm ? § Step-by-step problem-solving process § Solution achieved in finite amount of time Programming Fundamentals --> Ch 1. Problem solving 2

Problem Solving Process • Phase 1 - Analyze the problem § Outline the problem and its requirements § Design (algorithm) to solve the problem ( Flow chart, pseudo code) § Algorithm tracing • Phase 2 - Implement the algorithm § Implement the algorithm in code (in Programming Language Program) § Verify that the algorithm works • Phase 3 - Maintenance § Use and modify the program if the requirements changes Programming Fundamentals --> Ch 1. Problem solving 3

Analyze the Problem (1) Outline the problem and its requirements • • Understand the problem Understand problem requirements § § • Does program require user interaction? Does program manipulate data? What is the output? are all possible circumstances handled? If the problem is complex, divide it into subproblems § Analyze each subproblem as above Programming Fundamentals --> Ch 1. Problem solving 4

Analyze the Problem (1) Design Algorithm 1. Flowcharts 2. pseudo-code Programming Fundamentals --> Ch 1. Problem solving 5

• A Flowchart is § An algorithm graphical representation. § Written as a combination of the following graphical notations: Flow Chart Symbols Start and End Selection Input / output Calculation Programming Fundamentals --> Ch 1. Problem solving Data Flow 6

• Pseudo-code: <Algorithm name> // input ? // function? // Output? Begin <data definition> <actions> End The comment lines “//” Programming Fundamentals --> Ch 1. Problem solving 7

Analyze the Problem (1) Algorithm Tracing § § Draw flowchart Find all possible paths Check each path with appropriate input data Observed Outputs not conform to the expected ones error in the algorithm. Programming Fundamentals --> Ch 1. Problem solving 8

Analyze the Problem (2) Problem Example. Convert a student mark from decimal mode to ABC mode. Understand problem requirements § Is the problem statement complete and unambiguous? § Does program require user interaction? Input the mark § Does program manipulate data? covert mark Control Requirements (IF statement) § What is the output? The mark converted to A or B or C or error Is there subproblem? No § Programming Fundamentals --> Ch 1. Problem solving 9

Analyze the Problem (2) Efficiency: - an algorithm may work correctly but be inefficient – by taking more time and using more resources than required to solve the problem. - becomes more important for larger programs. Programming Fundamentals --> Ch 1. Problem solving 10

Analyze the Problem (3) Design Algorithm Discovery • To discover an algorithm is to solve the problem! 1. Working backwards (modification of an old solution) Example: Min of a and b is known. Deduce Max a and b. 2. Look for a related problem that has been solved before (similar solutions reuse) The precedent algorithm of mark conversion is for single student. It may be generalized to many students 3. Stepwise Refinement (new solution) § Break the problem into several sub-problems § Solve each subproblem separately § Produces a modular structure Programming Fundamentals --> Ch 1. Problem solving 11

Analyze the Problem (3) • Example. Making tea. Suppose we have a robot which carries out household tasks. We wish to program the robot to make a cup of tea. An initial attempt at an algorithm might be: 1. Put tea leaves in pot 2. Boil water 3. Add water to pot 4. Wait 5 minutes 5. Pour tea into cup Programming Fundamentals --> Ch 1. Problem solving 12

Design Algorithm Discovery Strategies Stepwise Refinement

Analyze the Problem(3) • the designer must know when to stop refining. • In this example the instruction Switch on kettle is directly executable by the robot, but that Fill kettle with water is not. • Experience will tell us when a step is directly implementable or not. • The above algorithm consists of a sequence of steps, executed exactly once and in order Programming Fundamentals --> Ch 1. Problem solving 14

Analyze the Problem(3) • Control requirements: while Another common requirement is the need for iteration. — Example. Repeat the mark conversion for a class room of 30 students. Each student having a unique student number from 1 to 30. Programming Fundamentals --> Ch 1. Problem solving 15

Implement the algorithm (Coding) • After testing your algorithm, you can code it in any programming language. • In our lab, we are going to use C++ language. Programming Fundamentals --> Ch 1. Problem solving 16

C++ Language Elements • The general form of a C++ program // File: filename // Program description # include compiler directives void main ( ) { declarations section executable statement section } Programming Fundamentals --> Ch 1. Problem solving 17

v Computer Stage: after completing the program, the computer must do the following: - Compilation: - Execution: Programming Fundamentals --> Ch 1. Problem solving 18

Stages of Compilation o Performed by a program called the compiler o Translates the preprocessor-modified source code into object code (machine code) o Checks for syntax errors and warnings o Saves the object code to a disk file o If any compiler errors are received, no object code file will be generated. o An object code file will be generated if only warnings, not errors, are received. Programming Fundamentals --> Ch 1. Problem solving 19

Compiler converts human readable language to a language which is understandable by the operating system/hardware

Execution • when the program become don’t has errors, the computer execute it to produce the ……output. Programming Fundamentals --> Ch 1. Problem solving 21

Implement the algorithm Verify that the algorithm works source of errors • Many errors made in: - analyzing the problem, - developing an algorithm, and/or - coding the algorithm Programming Fundamentals --> Ch 1. Problem solving 22

Implement the algorithm • Errors are of three types: . syntax errors. run-time errors. logic errors • Syntax errors: detected by the C compiler. source code does not conform to one or more of C’s grammar rules. examples of syntax errors: undeclared variable, … • Often one mistake leads to multiple error messages – can be confusing Programming Fundamentals --> Ch 1. Problem solving 23

Implement the algorithm • Run-time errors. detected and displayed by computer during execution. - Occur when program directs computer to perform illegal operation. Example: int x=y/0; - will stop program execution and display message • Logic errors. - caused by faulty algorithm - sign of error: incorrect program output - cure: thorough testing and comparison with expected results A logic error is referred to as a bug, so finding logic errors is called debugging. Programming Fundamentals --> Ch 1. Problem solving 24

Conclusions (Cont’d) Programming Fundamentals --> Ch 1. Problem solving 25