Programming Two Lecture 5 - Arrays 2013Feb12

7/28/2019 Programming Two Lecture 5 - Arrays 2013Feb12

1/26

Programming II - CMP1025

Lecture Five Arrays

By David W. [email protected]

University of Technology, Jamaica

February 12, 2013


2/26

Expected Outcome

At the end of this lecture, the student shouldbe able to:

Appreciate the concept of an array data type

Declare, define and use array variables

Demonstrate how arrays are passed to modules(C functions)

Manipulate arrays of characters (strings) usingthe character handling library and stringfunctions in a computer program


3/26

Topics

Atomic data types

Array data types

Declaring and defining array variables Using array variables

Passing array variables to a module

Arrays of characters Character string handling library functions


4/26

Atomic data types

Revision:

Data types are used to declare what type ofdata a variable will be allowed to store

Atomic data types are the primitive data typesin a language

Atomic data types are the simplest, most basic

data types in a language they cant bebroken down into any smaller data types


5/26

Atomic data types

Atomic data types only store one item of data at atime e.g.

int j = 10;

In this example j can only hold one value at a time e.g.10. If 11 is placed in j the old value of 10 is erased.

Opposite of composite data types:

Are new data types formed by combining other atomicand/or composite data types,

Can potentially store more than one value at a time


6/26

Atomic data types

There are only four (4) atomic data types in the Cprogramming language:

char : represents individual characters

int : represent an integer in the range -2,147,483,648to 2,147,483,647

float : represents a single precision floating pointnumber in the range 3.4 x 1038

double : represents a double precision floating pointnumber in the range 1.7 x 10308


7/26

Atomic data types

Modifiers for atomic data types:

short,

long,

signed,

unsigned

Qualifiers for atomic data types: const,

volatile


8/26

Array data types

An array is a collection or list of elements of thesame data type

The entire array is referenced by a single

identifier name the name of the array Individual elements in the array can be accessed

via its index or subscript

This index is the position of the element in thelist, starting from 0 for the first element

Array elements are always stored consecutively,so the element at index 1 is beside index 0, etc


9/26

Array data types

Array can have multiple dimensions, for example,a n x m matrix

This lecture will focus on single dimension arrays

(which have only a single row of data) A later lecture will examine multiple dimension

arrays

For each dimension, the index starts from 0

This is called zero-based indexing


10/26

Declaring and definingarray variables

Declaration Format:

DataType ArrayName[ArraySize];

e.g.

int Score[10]; //declare array Score to hold

//ten integers

Definition/initialization:

ArrayName[Index] = value;

e.g.

Score[0] = 50; //set the first element to 50.


11/26


//arrays declaration exampleint main(){

int Score[5];

int index;

Score[0] = 51;Score[1] = 89;Score[2] = 63;Score[3] = 92;Score[4] = 75;

for(index = 0; index < 5; ++index){

printf("%d\n",Score[index]);}

}

Array Score is just declaredhere, but it is not initialized

Initialization done separatelyhere


12/26


Declaration and Initialization Format:

DataType ArrayName[ArraySize] = {element1,element2, , elementN};

e.g.

//declare array A to hold ten integers, and//initialized the array to 1,2,3...10 respectively

int A[10] = {1,2,3,4,5,6,7,8,9,10};


13/26


//arrays declaration exampleint main()

{int Score[5] = {51,89,63,92,75};int index;



}

Declaration and initialization

done in the same line here

A loop is used here to iterate

through the elements of thearray and display them


14/26


//arrays declaration exampleint main(){

int Score[5] = {0};int index;



for(index = 0; index < 5; ++index)

{ scanf("%d",&Score[index]);}


printf("%d\n",Score[index]);

}}

Use a loop to display thecontents of the array

Use a loop to allow the userto enter 5 values for the array

Use a loop to redisplay thecontents of the array


15/26

Using array variables

Examples

int A[5]={1,2,3,4,5}; //initializes elements toA[0]=1, a[1] =2, a[2]=3, a[3]=4, a[4]=5

int A[5]={0}; //initializes all 5 elements to 0

float FA[3] = {9.10f, 9.58f, 9.23f};

scanf(%f, &FA[2]);

printf(The third element is %f,FA[2]);

double DA[3] = {9.10, 9.58, 9.23};

char CA[4] = {'A', 'B', 'C', 'D'};


16/26


To pass an array to a function, specify the nameof the array and its size in the function call

Consider the following array:

int Score[5] = {51,89,63,92,75}; //Declaration

To pass this array to a function Display()

Display(Score, 5); //array passed to function

To pass just a single element of the array, specifythe array name and element's index e.g.:

PrintTopScore(Score[3]); //only element 4 passed


17/26


#include int main(){




for(index = 0; index < 5; ++index)

{ scanf("%d",&Score[index]);}


printf("%d\n",Score[index]);

}}

#include void Display(int [ ], int);

int main(){

int Score[5] = {51,89,63,92,75};int i;Display(Score, 5);for(i = 0; i < 5; ++i){

scanf("%d",&Score[i]);}Display(Score, 5);

}void Display(int Arr[], int Size){

int index;for(index = 0; index < Size; ++index){

printf("%d\n",Arr[index]);

}}

These two programs do the same task but in the 2nd version, the array is passed to a function


18/26


#include int main(){


for(index = 0; index < 5; ++index){printf("%d\n",Score[index]);

}


scanf("%d",&Score[index]);}



}

#include void Display(int [ ], int);void InputScores(int [ ], int);int main(){

int Score[5] = {51,89,63,92,75};Display(Score, 5);

InputScores(Score, 5);Display(Score, 5);}void Display(int Arr[ ], int Size){

int index;for(index = 0; index < Size; ++index)

printf("%d\n",Arr[index]);}void InputScores(int Arr[ ], int Size){

int index;

for(index = 0; index < Size; ++index)

scanf("%d",&Arr[index]);}

These two programs do the same task but in the 2nd version, the array is passed to a function


19/26


#include void Display(int [ ], int);void InputScores(int [ ], int);int main(){

int Score[5] = {51,89,63,92,75};Display(Score, 5);

InputScores(Score, 5);Display(Score, 5);}void Display(int Arr[ ], int Size){

int index;for(index = 0; index < Size; ++index)

printf("%d\n",Arr[index]);}void InputScores(int Arr[ ], int Size){

int index;

for(index = 0; index < Size; ++index)

scanf("%d",&Arr[index]);}

Note how the array is represented in

the function prototype. The array nameIs optional

However, in the function header, the arrayname and the name of the size argumentare mandatory

Unlike normal variables, arrays are passed

by reference so any change made to thecontents of the array in the function arereflected in the original array

Address-of operator needed in scanf toread single integer into array


20/26

Arrays of characters

C doesn't have an explicit string data type

Instead, it uses an array of characters to representa string

e.g. the string hi class can be represented as:

char string1[ ]="hi class";

char string2[ ]={'h', 'i', ' ', 'c', 'l', 'a', 's', 's', '\0'};

char string3[9]={'h', 'i', ' ', 'c', 'l', 'a', 's', 's', '\0'};

Note '\0'(known as the NULL character) is alwaysplaced at the end of a character array to mark the

end of a string


21/26


char string1[ ]="hi class";

The '\0' is automatically placed at the end of the string inthis format

Size of string (8+1=9 chars) is automatically calculated

char string2[ ]={'h', 'i', ' ', 'c', 'l', 'a', 's', 's', '\0'};

The '\0' must be explicitly placed at the end of the string in

this format

Size of string (8+1=9 chars) is still automatically calculated

Individual elements delimited by single quote andseparated by comma, placed inside { }


22/26


//character string example#include

int main(){

char string1[] = "hi class";char string2[] = {'h', 'i', ' ', 'c', 'l', 'a', 's', 's', '\0'};

char string3[20];

printf("String one has %s\n", string1);printf("String two has %s\n", string2);

scanf("%s", string3);printf("String three has %s\n", string3);

fflush(stdin);gets(string3);printf("String three now has %s\n", string3);

puts("string three still contains ");puts(string3);

}

This program declares three

character arrays: string1,String2 and string3.

It displays the contents ofthe first two, then acceptsa string from the user usingscanf, and stores it in the

third array.

It then flushes the inputstream and accepts anotherstring into string3 usinggets, and then displaysit on the screen using puts.

Note:gets is not safe to useas is can cause bufferoverflow. Use getlineInstead.

Also fflush has some quirks.


23/26


//character string example#include

int main(){

char string1[] = "hi class";char string2[] = {'h', 'i', ' ', 'c', 'l', 'a', 's', 's', '\0'};

char string3[20];

printf("String one has %s\n", string1);printf("String two has %s\n", string2);

scanf("%s", string3);printf("String three has %s\n", string3);

fflush(stdin);gets(string3);printf("String three now has %s\n", string3);

puts("string three still contains ");puts(string3);

}

Declaration of the 3 arrays.

string3 in not initialized sowill contain garbage values

Display string1 and string2using printf

Read a word from the userInto string3 using scanf.Notice address of operator (&)is not placed in front of the arrayName, as done with othervariables

fflush clears the input bufferand gets reads a string fromthe user

puts displays a string on the

standard output device

h i h dli


24/26

Character string handlinglibrary functions

A wealth of string handling functions are found inthe string.h library, included with C

#include

Popular ones include:

strlen returns the size of a character string

strcmp compares two strings

strcat concatenate two strings

strcpy copies a string

A lot more string functions are found in string.h

Ch i h dli


25/26


strlen(str) returns the size/length of a characterstring not including the null character at the endof the string

strcmp(s1,s2) compares two strings andreturns 0 if s1 is equal to s2, negative number ifs1 < s2, and positive number if s1 > s2

strcat(s1,s2) concatenate two strings, the

result is s2 is joined to s1

strcpy(s1,s2) copies a string, the result is thecontents of s2 are copied into s1

Character string handling


26/26


#include

#include

int main(){

char string1[] = "hi class";char string2[] = {'h', 'i', ' ', 'c', 'l', 'a', 's', 's', '\0'};char string3[] = "bye class";

printf("The length of string 1 is %d\n", strlen(string1));printf("The length of string 2 is %d\n", strlen(string2));printf("The length of string 3 is %d\n", strlen(string3));

printf("Comparing string1 and string2 gives %d\n", strcmp(string1,string2));printf("Comparing string1 and string3 gives %d\n", strcmp(string1,string3));

printf("Comparing string3 and string1 gives %d\n", strcmp(string3,string1));

strcat(string2,string3);printf("Concatenting string2 and string3 gives %s\n", string2);

strcpy(string2,string3);printf("Copying string3 to string2 gives %s\n", string2);

}

Trace through thisprogram in yourmind to determine

what it will output,then actually run theprogram to see if theresults are what youexpected

Date post:	03-Apr-2018
Category:	Documents
Upload:	stephan-smith
View:	221 times
Download:	0 times

Programming Two Lecture 5 - Arrays 2013Feb12

Documents