StringsA string is a
sequence of characters. We have used strings in a number of examples in the
previous chapter. Any group of characters (Except double quote sign) defined
between double quotations marks is a string constant. A string constant is used
as the first parameter in a call to a printf () function.
Declaration
and initializing string variables
C does not have
string data type. A string is declared like an array of characters. The general
form of declaration of a string variable is
char string_name[size];
The size
determines the number of characters in the string_name. Some examples are:
char
name[20];
char
city[10];
When the
compiler assigns a character string to a character array, it automatically
appends a null character(‘\0’) at the end of the string. Therefore, the size of
the string should be equal to the maximum number of characters in the string
plus one.
Like numeric
arrays, character arrays can also be initialized when they are declared. C
permits a character array to be initialized in either of the following two
forms:
a. char city[10]=”
b. char
city[10]={‘k’,’a’,’t’,’h’,’m’,’a’,’n’,’d’,’u’};
C also permits
us to initialize a character array without specifying the number of elements.
In such cases, the size of the array will be determined automatically, based on
the number of elements initialized. For example char city[]=”kathmandu”; Now
let us write a simple program.
// program to illustrate difference between
character array and string
#include<stdio.h>
#include<conio.h>
void main()
{
char city1[10]=”kathamndu”;
char city2[10]={
‘k’,’a’,’t’,’h’,’m’,’a’,’n’,’d’,’u’};
char city3[]=”kathmandu”;
printf(“%s”,city1);
printf(“%s”,city2);
printf(“%s”,city3);
}
Output:
kathmandu
kathmandu
kathmandu
In the
introduction section of this chapter, we have seen that the printf() statement
only requires the address of the first character of character array to print
the string, This concept is demonstrated in the following program.
// program to illustrate the use of pointer
and string
#include<stdio.h>
#include<conio.h>
void main()
{
char city1[10]=”kathamndu”;
char city2[10]={
‘k’,’a’,’t’,’h’,’m’,’a’,’n’,’d’,’u’};
char city3[]=”kathmandu”;
char
*ptrcity1=city1;
char
*ptrcity2=city2;
char
*ptrcity3=city3;
printf(“%s\n”,ptrcity1);
printf(“%s\n”,ptrcity2);
printf(“%s\n”,ptrcity3);
}
Output:
kathmandu
kathmandu
kathmandu
In the program ,
we have assigned the addresses of the character array, city1,city2 and city3 to
the pointer to char variable ptrcity1, ptrcity2 and ptrcity3 respectively as a
result prtcity1, ptrcity2 and ptrcity3 hold addresses of the first element of
the array i.e. k. when these addresses are supplied as arguments to printf()
statement, it printed the strings so, printf statement needs only the first
address of character array.
//Reading string from terminal
#include<stdio.h>
void main()
{
char
name[20];
printf(“Enter
your full name\n”);
scanf(“%s”,name);
printf(“Your
name is :%s”,name);
}
Output:
Enter your
full name
Abc xyz
Your name
is: Abc
Another and more
convenient method of reading string of text containing white spaces is to use
the built in function gets().
// program to illustrate the use of gets()
and puts() functions
#include<stdio.h>
#include<conio.h>
void main()
{
char
name[20];
printf(“Enter
your full name\n”);
gets(name);
puts(name);
getch();
}
Output:
Enter your
full name\n”);
Abc xyz
Abc xyz
getch(),getche()
and getchar() functions
These are called
unformatted console input output functions. They are used to receive single character
from input console. So far, we have consistently used the scanf() function to
read a value from input console. But, the drawback of the scanf() function is
to read a value from input console. But, the drawback of the scanf() function
is that we must hit ENTER key before it accepts what we have typed. However, we
often want a function that will read a single character as it is typed without
waiting for the ENTER key to be hit. The getch() and getche() are two functions
which serve this purpose. These functions return the character that has been
most recently typed. The ‘e’ in the getche() function means it echoes(displays)
the character that you type on the screen. The getch() function returns the
character that you typed without echoing it on the screen. getchar() works in
similar fashion and echoes the character you typed on the screen but requires
ENTER key to be hit following the character that you typed.
#include<stdio.h>
#include<conio.h>
void main()
{
char ch;
printf("Press
any key to continue\n");
getch(); //
will not echo the character
printf("\n
Type any character\n");
ch=getche(); //will
echo the character typed
printf("\n
Type any character \n");
getchar(); //will
echo character, must followed by ENTER key
printf("\n
Continue(y/n)");
getch();
}
Output:
Press any
key to continue
Type any
character
a
Type any
character
g
Continue(y/n)
// program to print ASCII values of
alphabet
#include<stdio.h>
#include<conio.h>
void main()
{
char ch;
int i=1;
clrscr();
for(ch=65;ch<=122;ch++)
{
if(ch>90 && ch<97)
continue;
printf("%c:%4d\n",ch,ch);
}
getch();
}
String handling functions:-
Large number of
strings handling functions can be carried out for string manipulations. Some of
the most commonly used string handling functions are:
- strlen()
function
This function returns the length of
a given string. It finds the length of the string.
// program that shows use of strlen()
function
#include<stdio.h>
#include<conio.h>
void main()
{
int ln;
char
str[]=”
printf(“String
length using library function:”);
ln
=strlen(str);
printf(“%d\n”,
ln);
}
- strcpy() function
This
function copies the contents of one string to another
e.g
int length;
char str[]=”
char *sptr;
strcpy (sptr, str);
printf(“String is copied: %s\n”, sptr);
}
3. strcat() function-
This function
concatenates two strings resulting in a single string. It takes two arguments,
which are pointer to the two strings. The resultant string is stored in the
first string specified in the argument list.
e.g
{
char str1[]=”Hello”;
char str2[]=”Kathamndu”;
strcat(str1,str2);
printf(“After concatenation:%s \n”,str1);
}
4. strcmp() function:
This function
compares two strings. This function returns an integer determined by the
relationship between the strings given in its arguments. The integer value is 0
if both strings are equal, positive if first string is greater than second
string, negative if the first string is less than second string. The comparison
takes place on the basis of their ASCII values.
//
program to illustrate the use of strcmp() function.
#include<stdio.h>
#include<string.h>
#include<conio.h>
void main()
{
char
str1[]=”ramesh”,str2[]=”ramensh”,str3[]=”rajesh”;
int
check1,check2;
check1=strcmp(str1,str2);
check2=strcmp(str1,str3);
printf(“value
of check1:%d”,check1);
printf(“value
of check2:%d”,check2);
}
Output:
value of
check1:0
value of
check2:3
5. strupr() function
This function
converts a lower case string to upper case. It takes one argument, which is
pointer to first element of the string.
e.g
int
length, ln;
static
char str[]=”
printf
(“Conversion is %s”, strupr(str));
6. strlwr() function
This function
converts an upper case string to lower case. It takes one argument, which is
pointer to the first element of the string.
e.g.
int
length;
static
char str [] =”KATHMANDU”;
printf(“Conversion
is %s”, strlwr(str));
}
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