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CS 192Lecture 11Fall 2011

October 28-30, 2011

Ghufran Ahmed

Strings

•^

A collection of items of same type in contiguous memory

-^

One-dimensional array of type

char

e.g.

”hello”

•^

A string is in double quotes and is called literal string constant

-^

A string is terminated by the null character: ‘\0’ (a zero)

-^

Compiler automatically appends it at the end of string; signifiesend of string for the compiler

-^

char

str[6]

“hello”;

•^

str[5]

is what?

•^

char

a1[]=“abc”;

•^

char

a2[]={‘a’,

‘b’,

‘c’};

•^

char

a3[]={‘a’,

‘b’,

‘c’,

‘\0’};

•^

cout<<a1;

cout<<a2;

cout<<a3;

•^

Is

a2[]

a string?

•^

char

b[4]=“hi”;

b[3]

set to zero (null) as is

b[2]

Reading Strings from Keyboard

•^

There is a problem with previous program, if the string haswhitespace characters

(space, tab, newline)

-^

Use gets() to read a string from the keyboard. #include <stdio.h>

int main(){

char str[80];cout << "Enter a string: ";cout.flush();gets(str); // read a string from the keyboardcout << "Here is your string: ";cout << str<<“\n”;return 0;

}

/*

The

gets

function reads a line,

which consists of all characters up to andincluding the first newline character ('\n'). gets

then replaces the newline character

with a null character ('\0') before returningthe line. */

gets() Library Function

String Library Functions

==========================

strcpy(s1, s2)

Copies until \0 is moved. Contents of

s

overwritten

s

should have enough space. The value of

s

is returned

==========================

int main(){

char str[80];strcpy(str, "hello");cout << str;return 0;

}^

//^

Output is: hello

String Library Functions

==========================

strcat(s1, s2)

Appends

s

to the end of

s

and returns

s

.^ s

is unchanged

==========================

int main(){

char s1[20], s2[10];strcpy(s1, "hello");strcpy(s2, " there");strcat(s1, s2);cout << s1<<“\n”;return 0;

} //output?

String Library Functions^ ==========================

strmp(s1, s2)

•^

compares two strings

lexicographically

•^

returns 0 if they are equal (dictionary order)

•^

returns a +ve number if s1 is greater than s

•^

returns a -ve number if s1 is less than s

strcmp(“Zoo”, “ape”);

ASCII code has uppercase before lowercase

strcmp(“Zoo”, “zoo”);

// Output?

strcmp(s1, s2) …

bool password();int main(){

if ( password() )

cout << "Logged on.\n";

else

cout << "Access denied.\n";

return 0;

int main(){

char s[80];for(;;){

cout << "Enter a string: ";cout.flush();gets(s);if( !strcmp("quit", s) )

break;

} return 0;

}

strcmp(s1, s2) …

int main(){

char s[80]; do{ cout << "Enter a string:";gets(s);} while(strcmp("quit",s));

//other than 0 is true

return 0; }

String Library Functions

==========================

strlen(s)

returns the length of s

==========================

int main(){

char str[80];cout << "Enter a string: ";gets(str);cout << "Length is: " << strlen(str) <<"\n";return 0;

} //what is the output if we enter: this is cs

String/Numeric Conversion

n=atoi(s)

Converts

s

to integer

ln=atol(s)

Converts

s

to a long integer

fn=atof(s)

Converts

s

to a float

itoa(v,s,b)

Converts

v

integer of base

b

to a string

s

To Upper

char mystring[80] = "i am a string";int i=0;while ( mystring[i] ){^

// mystring[i] - ’a’ + ’A’

char upper = mystring[i] - (97 - 65);cout << upper;i++;

-^

Test condition of the for loop is simply thearray indexed by i

-^

Loop runs until it encounters the nullterminator.==================================

toupper()

tolower()

isalpha()

isdigit()

isspace()

ispunct()

Using Null Terminator

-^

The following declares an array of 30 strings

-^

Each having a maximum length of 80 characters

char str_array[30][80];

-^

In order to access an individual string, specifyonly the left index.

Arrays of Strings