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BIEN 001 Introduction to Biomedical Engineering Methods Module 1:Introduction to Computers, Flowcharting and Programming in C Roger H. Johnson, September 5, 2000 Objectives: Introduction to Computers and Computing Environment at Marquette. Develop problem-solving strategies through flow charting. Introduction to program development environment. Introduction to C language programming. Develop two real C programs and run them. Lectures 1-2: Computing History Computer Constituents Evolution of Programming Essential Programming Steps Syntax Develop Two Programs in C

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Computing History Blaise Pascal and the mechanical adder Pascal was a French genius and mathematician who died young after religious mania. In 1642 he invented a mechanical calculator to assist in the adding of long columns of numbers in his father’s tax office. His most important writing is Thoughts on Religion. Gottfried Wilhelm Leibnitz’ adder/multiplier German invention of 1673 (or1694) which used stepped-gear-wheels. Joseph Jacquard and his pasteboard loom cards 1812: Pasteboard card read by the loom. Hole pattern determined thread combinations. Charles Babbage and his analytical engine 1830’s: First the Difference Engine, which would have been two tons of brass, steel and pewter clockwork. 1840: Then the Analytical Engine which could decide between two courses of action. Steam-engine-powered, would read punched cards, compute, request cards with bell.

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Herman Hollerith and the census device 1890: Used punched cards to process census information and speed tabulation. Howard Aikens and the Mark I 1944: Harvard Mark I. Used mechanical counters and electromagnetic relays to control its operation. John Mauchly and John Eckert and the Eniac 1946: Huge vacuum-tube computer; part of the war effort. Ballistic computations and code-breaking. John Backus and FORTRAN 1954: First inovation to translate human-intelligible language into machine language. Kernighan and Ritchie and C 1970’s: Dominant language in scientific programming today. FORTRAN 77 persists and other language, such as Pascal, Basic, and Cobol are used in niches.

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Computer Constituents CPU = central processing unit = control unit + arithmetic and logical unit Memory Input Output CPU Arithmetic and logical unit Control unit Memory Input Output Control Unit: Controls timing and directs all computer operations. Arithmetic Logic Unit: Makes all decisions and performs calculations. Memory: Stores instructions and data live within the computer. Input: Devices which input information into memory. Output: Devices which print or display data from memory.

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Evolution of Programming Machine language: sequence of zero’s and one’s = “binary string”. (refer to handout on binary number system) Assembly language: uses keywords to stand for sequences of zero’s and one’s: “ADD” = One keyword is one line of code is one binary string is one instruction. Compiler level: (“high-level” resembles English) e.g. C = A + B for(i=1;i<5000;i++) {..... One line of code can contain several words and require many machine language instructions. Object oriented: New “pictorial” method we won’t get into.

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Essential Programming Steps 1) A clear statement of the problem: Decide what it is you really want to do. Helps to decide if computer is really the way to do it. 2) A rough or general solution algorithm: Write down in brief format the steps required to solve the problem. 3) A refined algorithm of the solution: More detailed sequence of steps. 4) A flowchart of the full solution process: Draw a block diagram or “flow diagram” of the computer program. 5) Computer language coding + documentation: A line-by-line written version of computer code. 6) Creation of a computer file of the coding: Type in the code using a text editor. 7) Compile and run the file: Type a command which creates the object file and the machine language version of code. 8) Obtain sufficient output to test the full solution algorithm for generality.

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An algorithm is a description of a solution method. Synonyms are “procedure”, “method”, “technique” or “(set of) rule(s)”. In the programming context, an algorithm must possess these characteristics: It must end after a finite number of steps. It must be describable by a finite sequence of steps or instructions. It must be capable of dealing with all members of a particular class of problem.

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A flowchart is a pictorial representation of an algorithm. Flowcharts are sometimes called “block diagrams” or “flow diagrams”. A flowchart is a schematic of the logic used in problem solution and, properly used, should aid in the development of a sound logical approach. A completed flowchart should exactly represent the sequence of steps coded into the program, and can help avoid a number of common programming errors.

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Flowchart Symbols:

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Casanova Flowchart Example:

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Meal-ordering Flowchart:

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Flowchart for Tuition Computation:

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Tuition Computation Flowchart with Nested Decision Loops:

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Tuition Computation Flowchart with Termination:

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Tuition Computation with Termination:

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Decision with a Three-way Branch:

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Balance Computation with Termination: Counter for Loop Termination:

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Example used in Lab 1: C program to solve two linear equations with two unknowns. Of the several methods to solve this problem, we choose to solve for x and y by the use of determinants. e.g. x + 2y = 5 5x - y = 3

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For the general case: Ax + By = C Dx + Ey = F

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It must be borne in mind that division by zero is not allowed. This would happen with parallel lines: x + 2y = 5 3x + 6y = 10

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and would also occur with coincident lines: x + 2y = 5 -2x -4y = -10

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Steps Required in Writing the Program: Steps 1 through 4 should be done before you come in to lab: 1) Statement of the problem. What we just did. 2) General Algorithm: an overall solution process which should consist of numbered steps. 3) Refined Algorithm: expand the general algorithm; add major variable names or formulas; add solution detail to the plan. 4) Flow Chart: give complete control process; supply minor control variables; use algorithm-defined variables and formulas; think through “what will happen if?”. 5) Program Coding: uses all of the above; supplies the input and output detail and documentation; provides adequate comments.

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Step 2) Example of General Algorithm: 1) Open data file. 2) Repeatedly 3) read coefficients 4) write system 5) calculate determinants 6) test for output case, process and output 7) End.

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Example of refined algorithm: 1.1 Query for input filename 1.2 Open input file 2.1 For all data 3.1 Read coefficients A, B, C, D, E, F 3.2 If end of data, go to Write system: Ax + By = C Dx + Ey = F 5.1 Den = AE-DB 5.2 Xnum = CE-FB 5.3 Ynum = AF-DC 6.1 If Den !=0, go to If Xnum=0, write “no unique solution” 6.3 If Ynum !=0, write “no solution” 6.4 Go to X = Xnum/Den 6.6 Y = Ynum/Den 6.7 Write “‘x =‘ X; ‘y=‘ Y.” 6.8 Go to End.

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