1. Overview of Computers and C Programming
Review Ch 1~2
Overview of Computers and C Programming
Dr. J.-Y. Pan
Dept. Comm. Eng.
Nat. Chung Cheng Univ.

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

3. Figure 1.3 Components of a Computer

4. Memory Memory cell Address Contents Stored program concept
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

5. Figure 1.4 1000 Memory Cells in Main Memory

6. Von Neumann architecture a definition from http://computing-dictionary
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.

7. 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

8. Hence, write in High-level languages
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

9. Figure 1.12 Entering, 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.

10. 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.

11. 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

12. 1.5 APPLYING THE SOFTWARE DEVELOPMENT METHOD
CASE STUDY
CONVERTING MILES TO KILOMETERS

13. 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 = kilometers

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

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

16. Question?
A good question deserve a good grade…

17. 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

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

19. Preprocessor directives
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

20. 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>

21. Part 2: Executable statements
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

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

23. Reserved Words A word that has special meaning in C Appendix E  背起來
int
main function returns an integer value
void
main function receives no data from the operating system
double
the memory cells store real numbers
return
control from the main function to the operating system
Appendix E  背起來

24. A word having special meaning but one that a programmer may redefine
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

25. 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

26. Programs in memory Figure 2
Programs in memory Figure 2.2 Memory(a) Before and (b) After Execution of a Program

27. Assignment Statement Figure 2.3 Effect of kms = KMS_PER_MILE * miles;

28. Output operation: The printf function Syntax Display for Function Call
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> ”);

29. Formatting Numbers in Program Output
Field width
the number of columns used to display a value
Value
Format
Displayed Output
234
%4d
▓234
-234
%5d
▓▓234
▓-234
%6d
▓▓▓234
▓▓-234
%1d
%2d

30. Formatting Values of Type double
Displayed Output
%5.2f
▓3.14
%4.2f
3.14
%3.2f
%5.1f
▓▓ 3.1
%5.3f
3.142
%8.5f ▓
.1234
0.12
-.006
-0.01
%8.3f ▓▓
%.3f
-0.006
%.4f

31. 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

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

33. Arithmetic operators, Appendix C, 背優先權
Category 
Operator 
Associativity 
Postfix 
() [] ->  
Left to right 
Unary 
+ - ! ~ (type) * & sizeof  
Right to left 
Multiplicative  
* / % 
Additive  
+ - 
Shift  
<< >> 
Relational  
< <= > >= 
Equality  
== != 
Bitwise AND 
& 
Bitwise XOR  ^ 
Bitwise OR  | 
Logical AND 
&& 
Logical OR 
|| 
Conditional 
?: 
Assignment 
= += -= *= /= %= >>= <<= &= ^= |= 
Comma  , 

34. 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)
Application
Example
Avoiding integer division
Average = (double)total_score /
(double)num_students;
Rounding a number
Rounded_x = (int)(x + 0.5)

35. 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);

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