Chapter 1: An Overview of Computers and Programming Languages

Chapter 1: An Overview of Computers and Programming Languages

Introduction Without software, the computer is useless Software is developed with programming languages – C is a programming language C suited for a wide variety of programming tasks C Programming: Program Design Including Data Structures, Sixth Edition 2

A Brief Overview of the History of Computers (cont’d.) Categories of computers – Mainframe computers – Midsize computers – Micro computers (personal computers) C Programming: Program Design Including Data Structures, Sixth Edition 3

Elements of a Computer System Hardware CPU Main memory Secondary storage Input/Output devices Software C Programming: Program Design Including Data Structures, Sixth Edition 4

Hardware CPU Main memory: RAM Input/output devices Secondary storage C Programming: Program Design Including Data Structures, Sixth Edition 5

Central Processing Unit and Main Memory Central processing unit – Brain of the computer – Most expensive piece of hardware – Carries out arithmetic and logical operations C Programming: Program Design Including Data Structures, Sixth Edition 6

Central Processing Unit and Main Memory (cont’d.) C Programming: Program Design Including Data Structures, Sixth Edition 7

Central Processing Unit and Main Memory (cont’d.) Random access memory – Directly connected to the CPU All programs must be loaded into main memory before they can be executed All data must be brought into main memory before it can be manipulated When computer power is turned off, everything in main memory is lost C Programming: Program Design Including Data Structures, Sixth Edition 8

Central Processing Unit and Main Memory (cont’d.) Main memory is an ordered sequence of memory cells – Each cell has a unique location in main memory, called the address of the cell Each cell can contain either a programming instruction or data C Programming: Program Design Including Data Structures, Sixth Edition 9

Secondary Storage Secondary storage: device that stores information permanently Examples of secondary storage: – – – – – – Hard disks Flash drives Floppy disks Zip disks CD-ROMs Tapes C Programming: Program Design Including Data Structures, Sixth Edition 10

Input/Output Devices Input devices feed data and programs into computers – Keyboard – Mouse – Secondary storage Output devices display results – Monitor – Printer – Secondary storage C Programming: Program Design Including Data Structures, Sixth Edition 11

Software Software: programs that do specific tasks System programs control the computer – Operating system monitors the overall activity of the computer and provides services such as: Memory management Input/output activities Storage management Application programs perform a specific task – Word processors – Spreadsheets – Games C Programming: Program Design Including Data Structures, Sixth Edition 12

The Language of a Computer Analog signals: continuous wave forms Digital signals: sequences of 0s and 1s Machine language: language of a computer; a sequence of 0s and 1s Binary digit (bit): the digit 0 or 1 Binary code (binary number): a sequence of 0s and 1s C Programming: Program Design Including Data Structures, Sixth Edition 13

The Language of a Computer (cont’d.) Byte: – A sequence of eight bits Kilobyte (KB): 210 bytes 1024 bytes ASCII (American Standard Code for Information Interchange) – 128 characters – A is encoded as 1000001 (66th character) – 3 is encoded as 0110011 C Programming: Program Design Including Data Structures, Sixth Edition 14

C Programming: Program Design Including Data Structures, Sixth Edition 15

The Evolution of Programming Languages Early computers were programmed in machine language To calculate wages rate * hours in machine language: 100100 010001 //Load 100110 010010 //Multiply 100010 010011 //Store C Programming: Program Design Including Data Structures, Sixth Edition 16

The Evolution of Programming Languages (cont’d.) Assembly language instructions are mnemonic Assembler: translates a program written in assembly language into machine language C Programming: Program Design Including Data Structures, Sixth Edition 17

The Evolution of Programming Languages (cont’d.) Using assembly language instructions, wages rate hours can be written as: LOAD rate MULT hour STOR wages C Programming: Program Design Including Data Structures, Sixth Edition 18

The Evolution of Programming Languages (cont’d.) High-level languages include Basic, FORTRAN, COBOL, Pascal, C, C , C#, and Java Compiler: translates a program written in a high-level language into machine language The equation wages rate hours can be written in C as: wages rate * hours; C Programming: Program Design Including Data Structures, Sixth Edition 19

Processing a C Program #include iostream using namespace std; int main() { cout "My first C program." endl; return 0; } Sample Run: My first C program. C Programming: Program Design Including Data Structures, Sixth Edition 20

Processing a C Program (cont’d.) To execute a C program: – Use an editor to create a source program in C – Preprocessor directives begin with # and are processed by the preprocessor – Use the compiler to: Check that the program obeys the language rules Translate into machine language (object program) C Programming: Program Design Including Data Structures, Sixth Edition 21

Processing a C Program (cont’d.) To execute a C program (cont'd.): – Linker: Combines object program with other programs provided by the SDK to create executable code Library: contains prewritten code you can use – Loader: Loads executable program into main memory – The last step is to execute the program Some IDEs do all this with a Build or Rebuild command C Programming: Program Design Including Data Structures, Sixth Edition 22

Processing a C Program (cont’d.) C Programming: Program Design Including Data Structures, Sixth Edition 23

Programming with the Problem Analysis–Coding–Execution Cycle Algorithm: – Step-by-step problem-solving process – Solution achieved in finite amount of time Programming is a process of problem solving C Programming: Program Design Including Data Structures, Sixth Edition 24

The Problem Analysis–Coding– Execution Cycle (cont’d.) Step 1: Analyze the problem – Outline the problem and its requirements – Design steps (algorithm) to solve the problem Step 2: Implement the algorithm – Implement the algorithm in code – Verify that the algorithm works Step 3: Maintenance – Use and modify the program if the problem domain changes C Programming: Program Design Including Data Structures, Sixth Edition 25

The Problem Analysis–Coding– Execution Cycle (cont’d.) Thoroughly understand the problem and all requirements – Does program require user interaction? – Does program manipulate data? – What is the output? If the problem is complex, divide it into subproblems – Analyze and design algorithms for each subproblem Check the correctness of algorithm – Can test using sample data – Some mathematical analysis might be required C Programming: Program Design Including Data Structures, Sixth Edition 26

The Problem Analysis–Coding– Execution Cycle (cont’d.) Once the algorithm is designed and correctness verified – Write the equivalent code in high-level language Enter the program using text editor C Programming: Program Design Including Data Structures, Sixth Edition 27

The Problem Analysis–Coding– Execution Cycle (cont’d.) Run code through compiler If compiler generates errors – Look at code and remove errors – Run code again through compiler If there are no syntax errors – Compiler generates equivalent machine code Linker links machine code with system resources C Programming: Program Design Including Data Structures, Sixth Edition 28

The Problem Analysis–Coding– Execution Cycle (cont’d.) Once compiled and linked, loader can place program into main memory for execution The final step is to execute the program Compiler guarantees that the program follows the rules of the language – Does not guarantee that the program will run correctly C Programming: Program Design Including Data Structures, Sixth Edition 29

Example 1-1 Design an algorithm to find the perimeter and area of a rectangle The perimeter and area of the rectangle are given by the following formulas: perimeter 2 * (length width) area length * width C Programming: Program Design Including Data Structures, Sixth Edition 30

Example 1-1 (cont’d.) Algorithm: – Get length of the rectangle – Get width of the rectangle – Find the perimeter using the following equation: perimeter 2 * (length width) – Find the area using the following equation: area length * width C Programming: Program Design Including Data Structures, Sixth Edition 31

Example 1-5 Calculate each student’s grade – 10 students in a class; each student has taken five tests; each test is worth 100 points Design algorithms to: – Calculate the grade for each student and class average – Find the average test score – Determine the grade Data: students’ names; test scores C Programming: Program Design Including Data Structures, Sixth Edition 32

Example 1-5 (cont’d.) Algorithm to determine the average test score: – Get the five test scores – Add the five test scores Suppose sum stands for the sum of the test scores – Suppose average stands for the average test score: average sum / 5; C Programming: Program Design Including Data Structures, Sixth Edition 33

Example 1-5 (cont’d.) Algorithm to determine the grade: if average is greater than or equal to 90 grade A otherwise if average is greater than or equal to 80 and less than 90 grade B otherwise if average is greater than or equal to 70 and less than 80 grade C otherwise if average is greater than or equal to 60 and less than 70 grade D otherwise grade F C Programming: Program Design Including Data Structures, Sixth Edition 34

Example 1-5 (cont’d.) Main algorithm is as follows: – totalAverage 0; – Repeat the following for each student: Get student’s name Use the algorithm to find the average test score Use the algorithm to find the grade Update totalAverage by adding current student’s average test score – Determine the class average as follows: classAverage totalAverage / 10 C Programming: Program Design Including Data Structures, Sixth Edition 35

Programming Methodologies Two popular approaches to programming design – Structured – Object-oriented C Programming: Program Design Including Data Structures, Sixth Edition 36

Structured Programming Structured design: – Dividing a problem into smaller subproblems Structured programming: – Implementing a structured design The structured design approach is also called: – Top-down (or bottom-up) design – Stepwise refinement – Modular programming C Programming: Program Design Including Data Structures, Sixth Edition 37

Object-Oriented Programming Object-oriented design (OOD) – Identify components called objects – Determine how objects interact with each other Specify relevant data and possible operations to be performed on that data Each object consists of data and operations on that data C Programming: Program Design Including Data Structures, Sixth Edition 38

Object-Oriented Programming (cont’d.) An object combines data and operations on the data into a single unit A programming language that implements OOD is called an object-oriented programming (OOP) language Must learn how to represent data in computer memory, how to manipulate data, and how to implement operations C Programming: Program Design Including Data Structures, Sixth Edition 39

Object-Oriented Programming (cont’d.) Write algorithms and implement them in a programming language Use functions to implement algorithms Learn how to combine data and operations on the data into a single unit called an object C was designed to implement OOD OOD is used with structured design C Programming: Program Design Including Data Structures, Sixth Edition 40

ANSI/ISO Standard C C evolved from C C designed by Bjarne Stroustrup at Bell Laboratories in early 1980s – Many different C compilers were available C programs were not always portable from one compiler to another In mid-1998, ANSI/ISO C language standards were approved C Programming: Program Design Including Data Structures, Sixth Edition 41

Summary Computer: electronic device that can perform arithmetic and logical operations Computer system has hardware/software – Central processing unit (CPU): brain – Primary storage (MM) is volatile; secondary storage (e.g., disk) is permanent – Operating system monitors overall activity of the computer and provides services – Various kinds of languages C Programming: Program Design Including Data Structures, Sixth Edition 42

Summary (cont’d.) Compiler: translates high-level language into machine code Algorithm: step-by-step problem-solving process; solution in finite amount of time Problem-solving process has three steps: – Analyze problem and design an algorithm – Implement the algorithm in code – Maintain the program C Programming: Program Design Including Data Structures, Sixth Edition 43

Summary (cont’d.) Structured design: – Problem is divided into smaller subproblems – Each subproblem is solved – Combine solutions to all subproblems Object-oriented design (OOD): a program is a collection of interacting objects – Object: data and operations on those data C Programming: Program Design Including Data Structures, Sixth Edition 44