1

Review of Class on Oct 12

2

Outline of Chapter 4

How to write a function? Function Prototypes Function Invocation Function Definition The return Statement

More about function Program Correctness: The assert() Macro Function Declarations from the Compiler’s Viewpoint Invocation and Call-by-Value Developing a Large Problem

3

How to write a function?

#include <stdio.h>void prn_message(void);void prn_message(void);int main(void){ prn_message();prn_message(); printf(“Back to main function\n”); return 0;}void prn_message(void)void prn_message(void){{ printf(“A message for you: “);printf(“A message for you: “); printf(“Have a nice day!\n”);printf(“Have a nice day!\n”); return;return;}}

How to give the compiler information about the function?

Function prototype:How to pass control to the function?

Function InvocationHow to specify the function?

Function DefinitionHow to get the control back?

return statement

4

How to write a function?Preprocessing directivesfunction prototype of fucntion1function prototype of fucntion2int main(void){ Body of function definition}Header of function1 definition{

Body of function definition}Header of function2 definition{

Body of function definition}

function invocations

5

How to write a function?

Example: write a code to computer the minimum value of three integers. Define a function min2 which compute the

minimum value of two integers. Define a function min3 which calls function

min2 to compute the minimum value of three integers.

6

#include <stdio.h> Preprocessing directivesFunction prototype of min2Function prototype of min3int main(void){ ……. …… Call function min3 ……

}Header of min2 definition{ Body of function definition}Header of min3 definition{

Body of function definition

(Call function min2)}

int min2(int a, int b);int min3(int a, int b, int c);int main(void){ printf("min of 11,23,24 is %d\n", min3(11,23,24)); return 0;}int min2(int a, int b){ if (a<b) return a; else return b;}int min3(int a, int b, int c){ int mofab = min2(a,b); return min2(mofab, c);}

7

Outline of Chapter 4

How to write a function? Function Invocation Function Definition The return Statement Function Prototypes

More about function Program Correctness: The assert() Macro Function Declarations from the Compiler’s Viewpoint Invocation and Call-by-Value Developing a Large Program

8

Program Correctness: The assert() Macro

C provides the assert() macro in assert.h to guarantee certain conditions assert(exp)

ensures the value of exp is trueif exp is false, the system prints out a

message and abort the program.

9

Function Declarations from the Compiler’s Viewpoint

Preprocessing directivesfunction prototype of fucntion1function prototype of fucntion2int main(void){ Body of function definition}Header of function1 definition{

Body of function definition}Header of function2 definition{

Body of function definition}

Preprocessing directivesHeader of function1 definition{

Body of function definition}Header of function2 definition{

Body of function definition}int main(void){ Body of function definition}

A good program style is to give either the function definition or the function prototype or both before a function is used

10

Invocation and Call-by-Value

Function Invocation

fun_name(exp1, exp2); All arguments are passed call-by-value

Each argument is evaluated, and its value is used locally in place of the corresponding formal parameter.

If a variable is passed to a function, the stored value of that variable in the calling environment is not changed.

11

#include <stdio.h>int min2(int a, int b);int min3(int a, int b, int c);

min.h

#include “min.h”int main(void){ printf("%d\n", min3(1,3,4) ); return 0;}

main.c

int min2(int a, int b){ if (a<b) return a; else return b;}int min3(int a, int b, int c){ int mofab = min2(a,b); return min2(mofab, c);}

min.c

f.h: function prototypesf1.c, f2.c, f3.c

function definitions

in each .c file#include “f.h”

gcc f1.c f2.c f3.c

gcc main.c min.c

Developing a Large Program

12

End of Chapter 4: FunctionRead 4.1- 4.12

13

Chapter 5

Character Processing

14

Outline

The Data Type CharInput and output characters

getchar() putchar()

end-of-file signal: EOF

15

The Data Type char

How character is stored in a machine? Each character is stored in one byte

according to a specific encoding.

Examples of character codes:ASCII

o A table of the ASCII code in Appendix E

EBCDIC

16

The Data Type char

Examples:How character ‘a’ is stored in ASCII code?

How many bits in one byte? 8

Appendix E A table of the ASCII code

bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0

0 1 1 0 0 0 0 1

17

The Data Type char

When a character is stored in a byte, the contents of that byte can be thought of

as either a character or as a small integer.

18

The Data Type char

Example: char c=‘a’;

c is character ‘a’c is a small integer represented in

binary form 01100001, o What is the decimal value of this small

integer? 97

bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0

0 1 1 0 0 0 0 1

19

The Data Type charWhen a character is stored in a byte, it can be thought of as either

a character or as a small integer.

‘a’: 01100001the decimal value of 0110001 is 97

#include <stdio.h>int main(){ printf("%c\n", 'a'); printf("%d\n", 'a'); printf("%d\n", 97); printf("%c\n", 97); if ('a'==97) printf("'a'==97\n"); else printf("'a'!=97\n");}

%a.outa9797a'a'==97

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The Data Type charWhen a character is stored in a byte, it can be thought of as either

a character or as a small integer.

‘A’: the decimal value of ‘A’ is 65

#include <stdio.h>int main(){ printf("%c\n", ‘A'); printf("%d\n", ‘A'); printf("%d\n", 65); printf("%c\n", 65); if (‘A'==65) printf("‘A'==65\n"); else printf("‘A'!=65\n");}

%a.outA6565A‘A'==65

21

The Data Type charWhen a character is stored in a byte, it can be thought of as either

a character or as a small integer.

#include <stdio.h>int main(){ printf("printf1: %c\n", '\n'); printf("printf2: %d\n", '\n'); printf("printf3: %c\n", 10); printf("printf4: %d\n", 10);}

% a.outprintf1: printf2: 10 printf3: printf4: 10%

‘\n’: the decimal value of ‘A’ is 10

22

The Data Type char

In ASCII, Character ‘1’ == int 1?

#include <stdio.h>int main(){ printf("%c \n", '1'); printf("%d \n", '1'); if (1=='1') printf("1=='1' \n"); else printf("1!='1' \n");}

% a.out1491!='1'

23

The Data Type char

In ASCII, Code for 0 through 9 are contiguous, letters A through Z are contiguous, and letters a through z are contiguous.the difference between a capital letter and the corresponding lowercase letter is 32.

#include <stdio.h>int main(){ printf("%c %d\n", 'a', 'a'); printf("%c %d\n", 'A', 'A'); printf("%d \n", 'a'-'A'); printf("%c \n", 'A'+32); printf("%c \n", 'a'-32); printf("%c \n", 'a'+3); printf("%c \n", 'A'+3); printf("%c \n", 'Y'+32);}

% a.outa 97A 6532aAdDy%

24

The Data Type char

Summary each character is stored in one byte it can be interpreted as either

a character or as a small integer.

In ASCII, Character ‘1’ != int 1Code for

o 0 through 9 are contiguous, o letters A through Z are contiguous, and o letters a through z are contiguous.

the difference between a capital letter and the corresponding lowercase letter is 32.

25

Outline

The Data Type CharInput and output characters

getchar() putchar()

EOF: end-of-file

26

Input and output characters — getchar() and putchar()

Read and Write characters Use format %c in printf and scanf functions printf(“%c”, ‘A’); char c; scanf(“%c”, &c);

27

Input and output characters — getchar() and putchar()

putchar() defined in stdio.h To write a character to the screen

#include <stdio.h>int main(){

putchar('H');putchar('e');putchar('l');putchar('l');putchar('o');putchar('\n');

}

% a.outHello%

28

Input and output characters — getchar() and putchar()

getchar(): reads a character from the keyboard defined in stdio.h c = getchar()

getchar() gets a character from the keyboard and assigns it to the variable c.

#include <stdio.h>int main(){

char c;c=getchar();putchar(c);putchar('\n');

}

% a.outdd%

scanf(“%c”, &c);

29

Outline

The Data Type CharInput and output characters

getchar() putchar()

EOF: end-of-file

30

end-of-file: EOF

Example: Get inputs from the keyboard and print out

each input twice on the screen

#include <stdio.h>int main(void){ char c; while (1){ c = getchar(); putchar(c); putchar(c); } return 0;}

How many times the while loop is executed?

Infinite loop

How to indicate the input is ended?

while(the input is not ended){

31

end-of-file: EOF

How to indicate the input is ended? User can use end-of-file signal to indicate

the end of the input.How to represent end-of-file signal in C

code?How to enter an end-of-file signal?

32

end-of-file: EOF

EOF in C code: end-of-file signal: EOF the value of EOF is system-dependent

int value -1 is often usedo Library stdio.h provides the following line:

#define EOF (-1)different systems can have different

values In order to avoid confusion, whatever is

used to signal the end of a file, it cannot be a value that represents a character.

33

end-of-file: EOF

Example: Get inputs from the keyboard and print out

each input twice on the screen; User enters EOF to end the input.

#include <stdio.h>int main(void){ int c; while ((c=getchar())!=EOF){ putchar(c); putchar(c); } return 0;}

The value of EOF cannot be a value that represents a character.In order to store the value of both characters (char) and EOF, c’s type should be int instead of char.

#include <stdio.h>int main(void){ char c; while (1){ c = getchar(); putchar(c); putchar(c); } return 0;}

34

end-of-file: EOF

How to input an end-of-file signal (EOF)? Unix: carriage return followed by a control-d MS-DOS: control-z

35

end-of-file: EOF

Summary end-of-file: EOF the value of EOF is system-dependent,

provided in stdio.h different systems can have different values

Whatever is used to signal the end of a file, it cannot be a value that represents a character.

Input EOF in Unix: carriage return followed by a control-d

36

Chapter 5

Summary each character is stored in one byte, and it

can be interpreted as either a character or as a small integer.

In ASCII, Code for 0 through 9 are contiguous, letters A

through Z are contiguous, and letters a through z are contiguous.

the difference between a capital letter and the corresponding lowercase letter is 32.

putchar() To write a character to the screen c = getchar()

getchar() gets a character from the keyboard and assigns it to the variable c.

EOF

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End of Chapter 5: Character ProcessingRead 5.1 – 5.8