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CS149D Elements of Computer Science

CS149D Elements of Computer Science. Ayman Abdel-Hamid Department of Computer Science Old Dominion University Lecture 11: 10/1/2002. Outline. Skip section 3.6 and 3.7 Overview of Computer Programming Process Overview of algorithms and programming languages

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CS149D Elements of Computer Science

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  1. CS149D Elements of Computer Science Ayman Abdel-Hamid Department of Computer Science Old Dominion University Lecture 11: 10/1/2002 CS149D Fall 2002

  2. Outline • Skip section 3.6 and 3.7 • Overview of Computer Programming Process • Overview of algorithms and programming languages • Should cover section 4.1 from Brookshear Text, and sections 1.1-1.2 from Etter Text CS149D Fall 2002

  3. Computer Programming • Computer program • A sequence of instructions to be performed by a computer • Computer programming • The process of planning a sequence of steps for a computer to follow • Programming Process • Problem-solving phase • Implementation phase • Maintenance phase CS149D Fall 2002

  4. Programming Process1/3 • Problem-solving phase • Analysis and specification ( understand and define problem, and what is expected of solution) • General solution (algorithm: a logical sequence of steps that solves the problem) • Verification (Follow steps to make sure solution solves the problem) • Implementation phase • Concrete solution (Program in a Programming language) • Testing (make sure the program produces the desired results) • Maintenance phase • Use Program • Maintain Program (meet changing requirements) CS149D Fall 2002

  5. Programming Process2/3 Analysis and Specification Concrete solution (Program) General solution (algorithm) Testing Verification Maintenance Phase Documentation: writing program documentation, and user manuals In “Programming and Problem Solving with C++”, 3rd Edition, Jones and Bartlett Publishers, 2002 CS149D Fall 2002

  6. Programming Process3/3 How about we take a shortcut and start the programming process by the implementation phase? Costly shortcut Develop a general solution (algorithm) first Think first and code later! CS149D Fall 2002

  7. Algorithm1/3 • Algorithm • An ordered set of unambiguous executable steps, defining a terminating process • A step-by-step procedure for solving a problem in a finite amount of time • Make a list of all positive integers • Arrange the list in descending order (from largest to smallest) • Extract the first integer from the list • What are the problems with these instructions? CS149D Fall 2002

  8. Algorithm2/3 • Difference between an algorithm and its representation • Analogous to difference between a story and a book • An algorithm is abstract and can be represented in many ways • Algorithm for converting from Celsius to Fahrenheit can be represented as • 1. F = (9/5) C + 32 (algebraic equation) • 2. “ Multiply the temperature reading in Celsius by 9/5 and then add 32 to the product” An algorithm can be represented using some sort of language 1950s, 1960s  represented using flowcharts pseudocode (precisely defined textual structures) CS149D Fall 2002

  9. Algorithm3/3 • An algorithm for starting the car • Insert the key in ignition • Make sure transmission is in Park (or Neutral) • Depress the gas pedal • Turn key to start position • If engine starts within six seconds, release key to ignition position • If engine does not start in six seconds, release key and gas pedal, wait ten seconds, and repeat steps 3 through 6, but not more than five times • If the car does not start, call the garage CS149D Fall 2002

  10. Programming Language1/3 • A set of rules, symbols, and special words used to construct a computer program. There are rules for syntax (grammar) and semantics (meaning) • Machine language • Binary-coded instructions • Closely coupled with design of computer hardware • Assembly language • Low-level programming language in which a mnemonic is used to represent each of the machine language instructions • We have seen an example in chapter 2 from Brookshear Text • We need an assembler • Translate an assembly language program into machine code CS149D Fall 2002

  11. Programming Language2/3 • High-level language • closer to English and other natural languages • C++, Java, C, Fortran, Ada, Pascal, COBOL, BASIC • We need a compiler • Translate a high-level language program into machine code • Source program • Program written in a high-level language • Object program • Machine language version of a source program • Difference between compilation and execution of a program CS149D Fall 2002

  12. Programming Language3/3 • Some programming languages are translated by an interpreter (some versions of BASIC) • Interpreter translates and executes each instruction in the source program • Java uses both a compiler and interpreter CS149D Fall 2002

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