CC-112-Lec.1.ppsx
- 1. CC-112 PROGRAMMING FUNDAMENTALS Lecture No.1 Introduction To Problem Solving Delivered By Aamir Shahzad
- 2. WHAT IS A PROGRAM ? A computer program is a set of computer instructions, which are used for solving a problem. The program directs the computer to perform the actions that are needed to arrive at a solution. The number of instructions required to solve a problem depends on the complexity of the problem. These instructions may range from a few to many hundreds or thousands. The computation might be something mathematical, such as solving a system of equations or finding the roots of a polynomial. But it can also be a symbolic computation, such as searching and replacing text in a document or (strangely enough) compiling a program.
- 3. PROGRAMMING: A WAY OF THINKING Combines features from mathematics, engineering, and natural science. Like mathematicians, computer scientists use formal languages to denote ideas (specifically computations). Like engineers, they design things, assembling components into systems and evaluating tradeoffs among alternatives. Like scientists, they observe the behavior of complex systems, form hypotheses, and test predictions.
- 4. PROGRAMMING: A WAY OF THINKING • The single most important skill for a computer scientist is problem solving. • Problem solving means: • The ability to formulate problems, think creatively about solutions, and express a solution clearly and accurately.
- 5. PROBLEMS? . . . • The problem is not that there are problems. The problem is expecting otherwise and thinking that having problems is a problem.“ Theodore Rubin • The best way to escape from a problem is to solve it.--Brendan Francis • Every problem contains within itself the seeds of its own solution.--Stanley Arnold • It isn't that they can't see the solution. It's that they can't see the problem.-- G. K. Chesterton • Problems are to the mind what exercise is to the muscles, they toughen and make strong. - Norman Vincent Peale
- 6. WHAT IS A PROBLEM (IN COMPUTING) A discrepancy between what is required and what exists. A computer program is meant to solve a problem. Think of a programming problem in the same light as you would think of a mathematical problem. It's not something bad(though some people may say otherwise). Rather, it is something that needs to be solved or a task that needs to be accomplished.
- 7. WHAT IS PROBLEM SOLVING? • Problem solving has long been recognized as one of the hallmarks of mathematics. • “Solving a problem means finding a way out of difficulty, a way around an obstacle, attaining an aim which was not immediately attainable.”
- 8. FOUR-STEP PROBLEM-SOLVING PROCESS 1. Understand the problem 2. Devise a plan 3. Carry out the plan 4. Look back
- 9. STEP-1: UNDERSTANDING THE PROBLEM • Can you state the problem in your own words? • What are you trying to find or do? • What are the unknowns? • What information do you obtain from the problem? • What information, if any, is missing or not needed?
- 10. STEP-2: DEVISING A PLAN (SOME STRATEGIES YOU MAY FIND USEFUL) • Look for a pattern. • Examine related problems and determine if the same technique can be used. • Examine a simpler problem to gain insight into the solution of the original problem. • Make a table or list. • Make a diagram. • Write an equation. • Use guess and check. • Work backward. • Identify a subgoal. • Use indirect reasoning. • Use direct reasoning.
- 11. STEP-3: CARRYING OUT THE PLAN • Implement the strategy or strategies. • Check each step of the plan as you proceed. • Keep an accurate record of your work. • Implement the strategy of strategies in step 2 and perform any necessary actions or computations. • Check each step of the plan as you proceed. This may be intuitive checking or a formal proof of each step. • Keep an accurate record of your work. Label each step.
- 12. STEP-4: LOOKING BACK CHECK THE RESULTS IN THE ORIGINAL PROBLEM • Interpret the solution in terms of the original problem. • Determine whether there is another method of finding the solution. • If possible, determine other related or more general problems for which the techniques will work.
- 13. DEVELOPMENT OF COMPUTER SOLUTION • Identify or Define the problem • Analyze the problem in terms of inputs, outputs, formulas, constants) • Design the Solution • Represent the most efficient solution in the form of an algorithm. • Implement (program coding) • Evaluate
- 14. IDENTIFY OR DEFINE THE PROBLEM In order for you to come up with an algorithm to solve a problem, you must first have a clear understanding of what the problem is. The first thing you have to do is to obtain a problem statement (a clear definition of the problem that needs to be solved). At this level it will usually be provided for you, but in the real world the programmer would have to work with his client to come up with one. Here are some (very simple) examples of problem statements:
- 15. ANALYZE THE PROBLEM We need to read it till we understand every detail We need to dissect the problem into its component parts (e.g. problems and sub-problems) We need to remove any ambiguity, extra information We need to determine our knowns and our unknowns We need to be aware of any assumptions we are making.
- 16. ANALYZE THE PROBLEM The Program Must Read Two Numbers And Print The Total Of The Two. Determining the input, output, processing and storage The next step in defining the problem is to break it down into its main components: 1. Inputs - the data you are provided with or have to obtain from the user. Some words that help you to identify the inputs are: read, input, enter, given, accept 2. Outputs - the results that should be produced 3. Processing - the tasks that must be performed, i.e. what must be done with the inputs to get the outputs 4. Storage - the data that must be stored
- 17. ANALYZE THE PROBLEM The Program Must Read Two Numbers And Print The Total Of The Two. • Inputs - The word 'read' tells us that the inputs will be in the form of two numbers. For reasons that will be explained later, it's helpful to give the inputs names, so we'll call them numl and num2. • Outputs - The desired result is the total, so we'll call the output 'total’. • Processing - Reading the two numbers is processing and so is printing the total. But is that everything? The total doesn't magically appear. You have to do something to the inputs to obtain the total. So there is an in- between step that is implied - calculating the total. • Storage - the data that must be stored
- 18. ANALYZE THE PROBLEM The Program Must Read Two Numbers And Print The Total Of The Two. • Defining diagrams • One way of illustrating the main components of a problem is by using a defining diagram. • A defining diagram is a table with three columns: 'Input', 'Processing' and 'Output'. • Consider the following problem statement: Write a program that reads two numbers and prints the total. • Even this simple statement requires some detective work to figure out the input, output and especially the processing. • the defining diagram would look like this: Input Processing Output Two Numbers, i.e. numl, num2 Read two numbers Total Calculate the total Print the total
- 19. DESIGN THE SOLUTION Developing the algorithm that solves the problem Identify alternative ways to solve the problem Select the best way to solve the problem from the list of alternative solutions List instructions that enable you to solve the problem using selected solution The algorithm is expressed a s flowchart or pseudo-code
- 20. PAYROLL EXAMPLE - ANALYSIS
- 21. PAYROLL EXAMPLE - DESIGN
- 22. PROGRAM COMPONENTS A few basic instructions appear in every language: Input - Get data from the keyboard, a file, or some other device. Output - Display data on the screen or send data to a file or other device. Math Perform basic mathematical operations like addition and multiplication. Conditional execution - Check for certain conditions and execute the appropriate sequence of statements. Repetition/Looping - Perform some action repeatedly, usually with some variation.
- 23. WHAT IS DEBUGGING? Programming errors are called bugs and the process of tracking them down and correcting them is called debugging. Three kinds of errors can occur in a program: 1. Syntax errors A program can only be executed if it is syntactically correct; otherwise, the process fails and returns an error message. syntax refers to the structure of a program and the rules about that structure. 2. Runtime errors So called because the error does not appear until you run the program. These errors are also called exceptions because they usually indicate that something exceptional (and bad) has happened. 3. Semantic errors If there is a semantic error in the program, it will run successfully, in the sense that the computer will not generate any error messages, but it will not do the right thing. It will do something else. Specifically, it will do what the programmer told it to do. But the written program does not solve the original problem. The meaning of the program (its semantics) is wrong.