Outline. Introduction. Arrays declarations and initialization. Const variables. Character arrays. Static arrays. Examples.

Transcription

1 Outline Introduction. Arrays declarations and initialization. Const variables. Character arrays. Static arrays. Examples. 1

2 Arrays I Array One type of data structures. Consecutive group of memory locations Same name and type Static data structure in which its size remain the same during the program execution. To refer to an element, specify Array name and position number Format: arrayname[ position number ] First element at position 0 n element array c: c[ 0 ], c[ 1 ] c[ n - 1 ] 2

3 Arrays II Array elements are like normal variables c[ 0 ] = 3; cout << c[ 0 ]; Performing operations in subscript. If x = 3, c[ 5 2 ] == c[ 3 ] == c[ x ] i th element in an array has the index (or subscript) of i 1. Array element i has a an index of i. The subscript must be an integer value, where it could be: Constant. Variable. Expression. A result of a function call. Subscript is always int variable or value 3

4 Arrays III Name of array (Note that all elements of this array have the same name, c) c[0] -45 c[1] 6 c[2] 0 c[3] 72 c[4] 1543 c[5] -89 c[6] 0 c[7] 62 c[8] -3 c[9] 1 Position number of the element within array c c[10] c[11]

5 Declaring Arrays Declaring arrays - specify: Name Type of array Number of elements Examples int c[ 10 ]; float hi[ 3284 ]; Declaring multiple arrays of same type Similar format as other variables Example int b[ 100 ], x[ 27 ]; 5

6 Arrays Initialization Two methods to initialize an array: Using a loop. Using an initializers list. Initializers int n[ 5 ] = { 1, 2, 3, 4, 5 }; If not enough initializers, rightmost elements become 0 If too many initializers, a syntax error is generated int n[ 5 ] = { 0 } Sets all the elements to 0 since the first element is initialized to 0 and the rest are implicitly initialized to 0. int array[4]={5} Sets the first element to 5 and the rest to zero. If size omitted, the initializers determine it int n[] = { 1, 2, 3, 4, 5 }; 5 initializers, therefore n is a 5 element array 6

7 1 // Fig. 4.4: fig04_04.cpp 2 // Initializing an array with a declaration 3 #include <iostream> 4 5 using std::cout; 6 using std::endl; 7 8 #include <iomanip> 9 10 using std::setw; int main() 13 { 14 int n[ 10 ] = { 32, 27, 64, 18, 95, 14, 90, 70, 60, 37 }; cout << "Element" << setw( 13 ) << "Value" << endl; for ( int i = 0; i < 10; i++ ) 19 cout << setw( 7 ) << i << setw( 13 ) << n[ i ] << endl; return 0; 22 } Element Value Notice how they array is declared and elements referenced. The Hashemite University 7

8 const Variables Also called named constants or read-only variables. Reserve space in memory. Must be initialized when declared to avoid getting a syntax error. A constant variable cannot be modified throughout the program after it is being declared. Arrays sizes are usually declared with type const since they are static (fixed). If you want to declare the size of an array using a variable this variable must be declared const, otherwise you will get a syntax error, e.g.: int x = 10; int c_class[x]; // syntax error //But const int x = 10; int c_class[x]; //Correct 8

9 1 // Fig. 4.7: fig04_07.cpp 2 // A const object must be initialized 3 4 int main() 5 { 6 const int x; // Error: x must be initialized 7 8 x = 7; // Error: cannot modify a const variable 9 10 return 0; 11 } Notice that const variables must be initialized because they cannot be modified later. Fig04_07.cpp: Error E2304 Fig04_07.cpp 6: Constant variable 'x' must be initialized in function main() Error E2024 Fig04_07.cpp 8: Cannot modify a const object in function main() *** 2 errors in Compile *** 9

10 Character Arrays I Strings is the same as array of characters. All strings end with NULL or '\0' Character array initialization: With string literal, Examples: char string1[] = "hello"; With initializers, Examples: char string1[] = { 'h', 'e', 'l', 'l', 'o', '\0 }; Input from keyboard char string2[ 10 ]; cin >> string2; Takes user input Side effect: if too much text entered, data written beyond array (i.e. read the first n-1 characters and the last character is set to \0) 10

11 Character arrays examples int main() { char arr[10]={'c','c'}; for(int i=0;i<10;i++) {cout<<arr[i];} return 0; } Output cc int main() { char arr[10]={ this is a test }; for(int i=0;i<10;i++) {cout<<arr[i];} return 0; } Syntax Error int main() { char arr[10]; cin>>arr //enter this is a test for(int i=0;i<10;i++) {cout<<arr[i];} return 0; } Output this ` ` ` This is the terminating string \0 and garbage values 11

12 Character Arrays II Subscripting is the same as for a normal array String1[ 0 ] is 'h' string1[ 2 ] is 'l' Remember that cin stop reading from keyboard at the first white space. If you enter a string with smaller size than the array size using cin, cin will automatically add a NULL at the end of the string within the array. cout stop printing an array of character when it reaches the \0. Character arrays that do not terminate with NULL (i.e. not strings) cannot be printed using cout, it will enter an infinite loop logical error. 12

13 1 // Fig. 4_12: fig04_12.cpp 2 // Treating character arrays as strings 3 #include <iostream> 4 5 using std::cout; 6 using std::cin; 7 using std::endl; 8 9 int main() 10 { 11 char string1[ 20 ], string2[] = "string literal"; cout << "Enter a string: "; 14 cin >> string1; 15 cout << "string1 is: " << string1 16 << "\nstring2 is: " << string2 17 << "\nstring1 with spaces between characters is:\n"; for ( int i = 0; string1[ i ]!= '\0'; i++ ) 20 cout << string1[ i ] << ' '; cin >> string1; // reads "there" 23 cout << "\nstring1 is: " << string1 << endl; cout << endl; 26 return 0; 27 } Enter a string: Hello there string1 is: Hello string2 is: string literal string1 with spaces between characters is: H e l l o string1 is: there Inputted strings are separated by whitespace characters. "there" stayed in the buffer. Notice how string elements are referenced like arrays. The Hashemite University 13

14 Static Arrays Similar to static storage variable you can define an array to be static. So this array will not be destroyed when you become outside the scope in which it exists. If you do not initialize a static array, by default the compiler will initialize all its elements to 0. 14

15 The Hashemite University 15

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17 Output 17

18 Notes Going outside the range of an array is a logical error in C++. int main() { char array[10]; cin>>array[20]; // logical error } There are additional examples of using arrays in the textbook, study them. 18