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Monday, Jan 20, 2002Kate Gregory with material from Deitel and Deitel Week 3 Questions from Last Week Hand in Lab 1 Arrays Pointers Strings Lab 2.

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Presentation on theme: "Monday, Jan 20, 2002Kate Gregory with material from Deitel and Deitel Week 3 Questions from Last Week Hand in Lab 1 Arrays Pointers Strings Lab 2."— Presentation transcript:

1 Monday, Jan 20, 2002Kate Gregory with material from Deitel and Deitel Week 3 Questions from Last Week Hand in Lab 1 Arrays Pointers Strings Lab 2

2 Monday, Jan 20, 2002Kate Gregory with material from Deitel and Deitel

3 Monday, Jan 20, 2002Kate Gregory with material from Deitel and Deitel Arrays A collection of items, all the same type, that can be treated as a unit or one at a time 10 integers 5 floating point numbers 100 characters

4 Monday, Jan 20, 2002Kate Gregory with material from Deitel and Deitel Memory arrangement c[6] c[0] c[1] c[2] c[3] c[11] c[10] c[9] c[8] c[7] c[5] c[4]

5 Monday, Jan 20, 2002Kate Gregory with material from Deitel and Deitel Declaring Arrays int scores[10]; char letters[26]; float ratios[5]; Size is fixed

6 Monday, Jan 20, 2002Kate Gregory with material from Deitel and Deitel Using Array Elements scores[i]++; cout << letters[4]; ratio[2] = 4.7;

7 Monday, Jan 20, 2002Kate Gregory with material from Deitel and Deitel No bounds checking in C++ int scores[10]; for (int i=0; i<20; i++) { scores[i] = 100; } Youre the programmer!

8 Monday, Jan 20, 2002Kate Gregory with material from Deitel and Deitel Bug prevention #define MAXSCORES 10 int scores[MAXSCORES]; for (int i=0; i< MAXSCORES; i++) { scores[i] = 100; } More readable, less error-prone Cant use a variable when declaring the array

9 Monday, Jan 20, 2002Kate Gregory with material from Deitel and Deitel Initializers int n[ 5 ] = { 1, 2, 3, 4, 5 }; Or just int n[] = { 1, 2, 3, 4, 5 };

10 Monday, Jan 20, 2002Kate Gregory with material from Deitel and Deitel Passing arrays to functions int total(int[] a); //... int numbers[] = {1,2,3,4,5}; int x = total(numbers);

11 Monday, Jan 20, 2002Kate Gregory with material from Deitel and Deitel Taking arrays in functions int total(int[] a) { int tot = 0; int limit = sizeof(a) / sizeof(int); for (int i=0; i

12 Monday, Jan 20, 2002Kate Gregory with material from Deitel and Deitel Pointers Address of a variable in memory They have a type int* p; char* s;

13 Monday, Jan 20, 2002Kate Gregory with material from Deitel and Deitel & operator & (address operator) gets address of operand int y = 5; int *yPtr; yPtr = &y; // yPtr gets address of y yPtr y 5 yptr y 5 Address of y is value of yptr

14 Monday, Jan 20, 2002Kate Gregory with material from Deitel and Deitel * operator * (indirection/dereferencing operator) –Gives access to what the pointer points to –*yptr returns y (because yptr points to y ) –* can be used for assignment *yptr = 7; // changes y to 7 * and & are inverses –They cancel each other out

15 Monday, Jan 20, 2002Kate Gregory with material from Deitel and Deitel Pointers and Arrays int scores[10]; x = scores[3]; x++; y = scores; y++;

16 Monday, Jan 20, 2002Kate Gregory with material from Deitel and Deitel Pointers and Arrays scores[1] = 2; int* p = scores; p++; *p = 2; Adding is cheaper than multiplying

17 Monday, Jan 20, 2002Kate Gregory with material from Deitel and Deitel String = Array of Characters char word[] = {K,a,t,e,\0}; char word[] = Kate; Note that \0 and 0 are different. Null terminated strings

18 Monday, Jan 20, 2002Kate Gregory with material from Deitel and Deitel Accessing characters cout << word; cout << word[0]; word[0] = L; Note single quotes

19 Monday, Jan 20, 2002Kate Gregory with material from Deitel and Deitel Strings and pointers for (char* p = word; *p; p++) { cout << *p; }

20 Monday, Jan 20, 2002Kate Gregory with material from Deitel and Deitel Arrays of Pointers char *suit[ 4 ] = { "Hearts", "Diamonds", "Clubs", "Spades" }; –Strings are pointers to the first character –char * – each element of suit is a pointer to a char –The strings are not actually stored in the array suit, only pointers to the strings are stored –suit array has a fixed size, but strings can be of any size

21 Monday, Jan 20, 2002Kate Gregory with material from Deitel and Deitel Arrays of Pointers suit[3] suit[2] suit[1] suit[0]Hearts \0 Diamonds Clubs Spades

22 Monday, Jan 20, 2002Kate Gregory with material from Deitel and Deitel Multi Dimensional Arrays Tables with rows and columns ( m by n array) Like matrices: specify row, then column Row 0 Row 1 Row 2 Column 0Column 1Column 2Column 3 a[ 0 ][ 0 ] a[ 1 ][ 0 ] a[ 2 ][ 0 ] a[ 0 ][ 1 ] a[ 1 ][ 1 ] a[ 2 ][ 1 ] a[ 0 ][ 2 ] a[ 1 ][ 2 ] a[ 2 ][ 2 ] a[ 0 ][ 3 ] a[ 1 ][ 3 ] a[ 2 ][ 3 ] Row subscript Array name Column subscript

23 Monday, Jan 20, 2002Kate Gregory with material from Deitel and Deitel Multi Dimensional Arrays Initialization int b[2][2] = { { 1, 2 }, { 3, 4 } }; –Initializers grouped by row in braces –If not enough, unspecified elements set to zero int b[2][2] = { { 1 }, { 3, 4 } }; Referencing elements –Specify row, then column cout << b[0][1];

24 Monday, Jan 20, 2002Kate Gregory with material from Deitel and Deitel String Library Functions originally from C –strlen –strcat –strcpy –strcmp –strtok Dont reinvent the wheel

25 Monday, Jan 20, 2002Kate Gregory with material from Deitel and Deitel For Next class Complete Lab 2 –Late penalty is TERRIBLE Read chapter 6


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