1. CSE 303 Concepts and Tools for Software Development
CSE 303 Lecture 9
10/16/2006
CSE 303 Concepts and Tools for Software Development
Richard C. Davis UW CSE – 10/16/2006
Lecture 9 – C Arrays and Strings

2. Administravia Homework #2 is due! Societal Implications Assignment #1
Due next lecture!
10/16/2006
CSE 303 Lecture 9

3. Tip of the Day Emacs Macros C-x ( : Start recording Macro
All keystrokes recorded
C-x ) : Stop recording Macro
C-x e : run macro
C-u <num> C-x e : run macro <num> times
C-u runs any command multiple times
10/16/2006
CSE 303 Lecture 9

4. Last Time C-Program Structure Syntax Printf Declarations and Scope
Argument Passing
Syntax
Booleans and arrays
Confusing Cases
Printf
10/16/2006
CSE 303 Lecture 9

5. Today Syntax Command-line Arguments Type names Arrays Strings
10/16/2006
CSE 303 Lecture 9

6. Type Names Can usually tell from declaration
int i; : i has type (int)
float f; : f has type (float)
Pointers are a little more confusing
int *p; : p has type (int*) or (int *)
int **p; : p has type (int**) or (int **)
int* p; : p has type (int*) or (int *)
int* p,q; : q has type (int)
We’ll see later when we discuss casting
10/16/2006
CSE 303 Lecture 9

7. Arrays in C Array : group of memory locations with Example: Same name
Same type
Example:
int i;
int c[3];
int j=23;
for (i=0; i<3; i++) {
c[i]=0; }
Stack i 3
c[0]
Increasing Addresses
c[1]
c[2] j 23
Note: Outside of the array, the order of variables is not defined.
10/16/2006
CSE 303 Lecture 9

8. Array Bounds Checking No array bounds check
Not done by compiler
Not done by run time system
You must add checks or live without them
Big source of errors
10/16/2006
CSE 303 Lecture 9

9. Pointer Arithmetic int i; int c[3]; int j=23; for (i=0; i<3; i++) {
printf("%d\n", c[i]);
printf("%d\n", *(c+i)); }
Type of array name is pointer!
Refers to address of first element in array
Examples in simpleArray.c
Stack i 3 c
c[0]
c+1
c[1]
c+2
c[2] j 23
10/16/2006
CSE 303 Lecture 9

10. Example 1 c[0] = 13; c[2] = 42; int *p = &c[4]; *p = 54; p++; *p = 64;
Stack
c[0] 1 2 3 4 5 6 7 8
10/16/2006
CSE 303 Lecture 9

11. Example 1 c[0] = 13; c[2] = 42; int *p = &c[4]; *p = 54; p++; *p = 64;
Stack
c[0] 13 1 42 3 4 5 6 7 8
10/16/2006
CSE 303 Lecture 9

12. Example 1 c[0] = 13; c[2] = 42; int *p = &c[4]; *p = 54; p++; *p = 64;
Stack
c[0] 13 1 42 3 p 4 5 6 7 8
10/16/2006
CSE 303 Lecture 9

13. Example 1 c[0] = 13; c[2] = 42; int *p = &c[4]; *p = 54; p++; *p = 64;
Stack
c[0] 13 1 42 3 p 54 5 6 7 8
10/16/2006
CSE 303 Lecture 9

14. Example 1 c[0] = 13; c[2] = 42; int *p = &c[4]; *p = 54; p++; *p = 64;
Stack
c[0] 13 1 42 3 54 p 5 6 7 8
10/16/2006
CSE 303 Lecture 9

15. Example 1 c[0] = 13; c[2] = 42; int *p = &c[4]; *p = 54; p++; *p = 64;
Stack
c[0] 13 1 42 3 54 p 64 6 7 8
10/16/2006
CSE 303 Lecture 9

16. Example 2 int i; for (i = 0; i <= 8; i++) { c[i] = c[i] + 10; }1 2 3 4 5 6 7 8
int i;
for (i = 0; i <= 8; i++) {
c[i] = c[i] + 10; } c 10 11 12 13 14 15 16 17 18
10/16/2006
CSE 303 Lecture 9

17. Example 3 int i; for (i = 0; i <= 8; i++) { *(c+i) = *(c+i) + 10; }1 2 3 4 5 6 7 8
int i;
for (i = 0; i <= 8; i++) {
*(c+i) = *(c+i) + 10; } c
c+1
c+3 c 10 11 12 13 14 15 16 17 18
10/16/2006
CSE 303 Lecture 9

18. Example 4 int *p; for (p = c; p <= c+8; p++) { *p = *p + 10; } c[0]1 2 3 4 5 6 7 8
int *p;
for (p = c; p <= c+8; p++) {
*p = *p + 10; } c
c+8 c 10 11 12 13 14 15 16 17 18
10/16/2006
CSE 303 Lecture 9

19. Passing Arrays to Functions
To pass array to function:
Give name without brackets
Common idiom: pass size in other arg
Example: modify(c,size);
Two function definition styles
void modify(int c[], int size);
void modify(int *c, int size);
Examples in arrayArg.c
10/16/2006
CSE 303 Lecture 9

20. Strings Strings: Null terminator: no need to specify size Problems:
An array of characters
Terminated with "null character"
Denoted with '\0'
Character with ASCII value 0
Null terminator: no need to specify size
Problems:
Size of array must include space for '\0'
Common bug: Overwrite '\0'
10/16/2006
CSE 303 Lecture 9

21. String Constants String Constants have type (char*)
Automatically null terminated
Example: char *str = "Hello";
str
'H'
'e'
'l'
'l'
'o'
'\0'
10/16/2006
CSE 303 Lecture 9

22. string.h Various string utility functions Example
See them with "man string"
Also on p470 of Programming in C
Example
char s1[20] = "blue ";
char s2[] = "gray";
char *s3 = strcat(s1, s2);
10/16/2006
CSE 303 Lecture 9

23. Arrays of Ponters Common idiom: combining multiple values
char *s[3] = { "Hello", "World", "!" };
'H'
'e'
'l'
'l'
'o'
'\0'
s[0]
s[1]
'W'
'o'
'r'
'l'
'd'
'\0'
s[2]
'!'
'\0'
10/16/2006
CSE 303 Lecture 9

24. Command Line Arguments
Main has other forms
int main(int argc, char** argv);
int main(int argc, char* argv[]);
argc holds number of strings (first is cmd)
argv holds strings
Note use of common idioms
array + length
array of pointers
Examples in commandLine.c
10/16/2006
CSE 303 Lecture 9

25. Summary Syntax Command-line Arguments Type names Arrays Strings
10/16/2006
CSE 303 Lecture 9

26. Reading Programming in C Chapter 7: Arrays Chapter 10: Strings
pp : Pointers and Arrays
pp : Command-Line Arguments
10/16/2006
CSE 303 Lecture 9

27. Next Time Structs The Heap Manual Memory Management 10/16/2006
CSE 303 Lecture 9