Understanding Computer Architectures and C Programming

ReviewCh 1~2 Overview of Computers and C Programming Dr. J.-Y. Pan Dept. Comm. Eng. Nat. Chung Cheng Univ. http://ant.comm.ccu.edu.tw jypan@comm.ccu.edu.tw

Outline • Von Neumann architecture • Computer languages • Software developing method • Applying the method • Case study:CONVERTING MILES TO KILOMETERS

Figure 1.3 Components of a Computer

Memory • Memory cell • an individual storage location • Address • relative position in memory • Contents • the data stored in a memory cell • Stored program concept • an ability to store program instructions in main memory for execution • We can change the computer’s operation by storing a different program in memory

Figure 1.41000 Memory Cells in Main Memory

Von Neumann architecturea definition fromhttp://computing-dictionary.thefreedictionary.com/ • Has a random-access memory (RAM) • which means that each successive operation can read or write any memory location, independent of the previous access. • Has a central processing unit (CPU) • The CPU has a set of registers and a set of built-in operations (its instruction set). • The CPU can interpret the contents of memory either as instructions or as data according to the fetch-execute cycle.

Central Processing Unit • Retrieves each instruction in sequence (called fetching an instruction) • Interprets the instruction to determine what should be done and then retrieves any data needed to carry out that instruction • Performs the actual manipulation, or processing, of the data it retrieved • Store the results in main memory

Computer languages • Software developers rarely write in the language directly understood by a computer • The machine language is a collection of binary numbers, not easy to understand by human • It is not standardized, different for different CPU • Hence, write in High-level languages • That combine algebraic expressions and symbols taken from English • Computers do NOT understand it… • Translation…By a compiler

Figure 1.12Entering, Translating, and Running a High-Level Language Program 記得，要常常存檔 The loader must copy all its instructions into memory and direct the CPU to begin execution with the first instruction.

Figure 1.13 Flow of Information During Program Execution As the program executes, it takes input data from one or more sources and sends results to output and/or secondary storage devices. Although the instructions normally are executed in sequence, it is possible to have the CPU skip over some instructions or execute some instructions more than once.

Software development method • Specify the problem requirements • State the problem clearly and gain a clear understanding of what is required for its solutions • Analyze the problem • Identify the problem Input/Output/Extra_requirements • Design the algorithm to solve the problem • Develop a list of steps (called algorithm) to solve it • Implement the algorithm • Convert each algorithm step into statements in C • Test and verify the completed program • Maintain and update the program • Modify a program to remove previously undetected errors and to keep it up-to-date

1.5 APPLYING THE SOFTWARE DEVELOPMENT METHOD CASESTUDY CONVERTING MILES TO KILOMETERS

Problem (Specify the problem requirements) • Your summer surveying job requires you to study some maps that gives distances in kilometers and some use miles. You and your coworkers prefer to deal in metric measurements. Write a program that performs the necessary conversion. • Analysis (Analyze the problem) • Purpose : Conversion from miles to kilometers. • To solve this problem, you need to know the relationship between miles and kilometers. • Data Requirements • Problem input ：miles /* The distances in miles */ • Problem output：kms /* The distances in kilometers */ • Relevant Formula : 1 mile = 1.609 kilometers

Design (Design the algorithm to solve the problem) • Algorithm • Get the distance in miles • Convert the distance to kilometers • Display the distance in kilometers • Algorithm with refinements • Get the distance in miles • Convert the distance to kilometers 2.1 The distance in kilometers is 1.609 times the distance in miles • Display the distance in kilometers • Implementation (Figure 1.14) (talks in Ch3) • Testing

Figure 1.14 Miles-to-Kilometers Conversion Program Step 1 Step 2 Step 3

Question? • A good question deserve a good grade…

Outline (Part 2) • C language elements • A running program, what happens? • Syntax and semantics • Input and output • Arithmetic operators • Program-Controlled Input and Output Files

Figure 2.1 C Language Elements in Miles-to-Kilometers Conversion Program

2.1 C Language Elements • Preprocessor • a system program that modifies the text of a C program before it is compiled • Preprocessor directives • commands that provides instructions to the C preprocessor • Library • a collection of useful functions and symbols that may be accessed by a program • each library has a standard header file

Preprocessor Directives(1/2) • #include • gives a program access to a library • <stdio.h> • standard header file • include printf、 scanf #include <stdio.h> • notify the preprocessor that some names used in the program are found in <stdio.h>

Function Main(1/2) Contains two parts Part 1: Declarations • the part of a program that tells the compiler the names of memory cells in a program Part 2: Executable statements • program lines that are converted to machine language instructions and executed by the computer

Function Main (2/2) • Syntax： int main(void) { /* function body */ printf(“Hello world\n”); return(0); }

Reserved Words • A word that has special meaning in C • Appendix E 背起來

Standard Identifiers • A word having special meaning but one that a programmer may redefine • In Figure 2.1, the standard identifiers printf and scanf are names of operations defines in the standard input/output library. • Appendix B shows ANSI C standard libraries • P.800~801, stdio.h所列之functions • P.799, math.h所列之functions • P.802, string.h所列之functions (教到字串時請自學) • 自行參考其功用，大略記一下

User-Define Identifiers • Syntax rules • An identifier must consist only of letters, digits, and underscores • An identifier cannot begin with a digit • A C reserved word cannot be used as an identifier • An identifier defined in a C standard library should not be redefined • 大小寫不一樣 • Rate, rate, RATE • Wildly adopted in industry uses all uppercase letters in the names of constant macros

Programs in memoryFigure 2.2 Memory(a) Before and (b) After Execution of a Program

Assignment StatementFigure 2.3 Effect of kms = KMS_PER_MILE * miles;

Output operation: The printf functionSyntax Display for Function Call • Syntax: • printf(format string, print list); • printf(format string); • Examples: • printf(“I am %d years old, and my gpa is %f\n”, age, gpa); • printf(“Enter the object mass in grams> ”);

Formatting Numbers in Program Output • Field width • the number of columns used to display a value

Formatting Values of Type double

Input operation: The scanf Functon • scanf(“%lf”, &miles); (Figure 2.5) • scanf(“%c%c%c”, &letter_1, &letter_2,&letter_3); (Figure 2.6) • & • The C address-off operator • Tell the scanf function where to find each variable into which it is to store a new value Beware the difference between SCANF and PRINTF in input arguments

Figure 2.5Effect of scanf("%lf", &miles);

Arithmetic operators, Appendix C, 背優先權

Type Conversion through Casts • type cast • converting an expression to a different type by writing the desired type in parentheses in front of the expression • Table 2.9 (Page 63, 課本有錯)

Program-Controlled Input and Output Files • declare a file pointer variable • FILE *inp , /* pointer to input file */ *outp ; /* pointer to output file */ • the calls to function fopen • inp = fopen(“b:distance.dat”, “r” ) ; • outp = fopen(“b:distance.out”, “w”) ; • use of the functions • fscanf(inp, “%lf”, &miles); • fprintf(outp, “The distance in miles is %.2f. \n”, miles); • end of use • fclose(inp); • fclose(outp);

Figure 2.14Miles-to-Kilometers Conversion Program with Named Files

Understanding Computer Architectures and C Programming