Strings
Topics
• String Libraries
• String Operations
• Sample Program
Reading
• Sections 8.1 - 8.7
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String
• A string is a character array that has a marker to
show where the data ends, when the array is
larger than the data.
char firstname[ 50 ] = “Sue”;
• The array firstname is 50 characters long, but the
data is only four characters long. You must count
the marker.
• The marker is character that is set to the number
zero. (Sometimes called a null terminator.)
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Array Constraint
• There are now built-in operators to
manipulate arrays, except to initialize them
when you declare the array:
char firstname[ 50 ] = “Sue”;
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Missing Operators
• There is no string assignment operators.
• There are not string comparison operators.
• There are not string combination operators.
• However, there are built-in functions to do
this common tasks.
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Built-in String Functions
• String assignment:
strcpy( destination, source )
char name[ 25 ]; /* contains nothing */
strcpy( name, “Hilton” ); /* name now
contains “Hilton” */
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Built-in String Functions (cont’d)
• String comparison:
strcmp( strA, strB );
If strA comes after strB, the function returns a positive
number.
o Is strB comes last, the function returns a negative
number.
o If strA and strB are the same thing, the function returns
a zero.
result = strcmp( “CMSC”, “IFSM” ); /* negative */
result = strcmp( “IFSM”, “CMSC” ); /* positive */
result = strcmp( “CSMC”, “CMSC” ); /* zero */
o
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Built-in String Functions (cont’d)
• String combination:
strcat( destination, source )
o
o
The source is not changed.
The destination contain exactly what it had before plus
what was in the source. Nothing else is added. NOTE:
If you are combining a first name and last name for a
full name, you must use another strcat to add the space
between them:
strcpy( fullName, firstName);
strcat( fullName, “ “ );
strcat( fullName, lastName );
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Built-in String Functions (cont’d)
• Extracting words (tokens) from a string:
/* get the first token (delimited by a blank) */
printf( "%s\n", strtok( b, " " ) );
/* This is more useful after you learn to use
pointers. */
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Built-in String Functions (cont’d)
• What if I want to get a menu choice, that is the
numbers 1 to 4 or the char ‘q’? Use getchar( ) to
get the menu choice, check for ‘q’ and if it is not,
then convert it to a number.
/* convert a string (ASCII) to an integer */
printf( "%d\n", atoi( "1234" ) );
/* convert a string (ASCII) to a float */
printf( "%f\n", atof( "1234.5678" ) );
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Built-in String Functions (cont’d)
• How long is the data in the string (not
counting the null terminator)?
stringSize = strlen( strA );
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String Libraries
#include files:
#include <stdlib.h>
/* needed by atoi( ) and atof( ) */
#include <string.h>
/* needed by str...( ) functions */
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Sample Program
#include <stdio.h>
#include <stdlib.h> /* needed by atoi( ) and
atof( ) */
#include <string.h> /* needed by str...( )
functions */
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Sample Program (cont’d)
int main( void )
{
char a[ 100 ] = "Excellence";
char b[ 100 ];
char c[ 100 ] = "Failure";
int result;
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Sample Program (cont’d)
/* Make sure the array a is as expected */
printf( "string a is >%s<\n", a );
/* assign a to b */
strcpy( b, a );
printf( "After strcpy(b, a), string b is now
>%s<\n", b );
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Sample Program (cont’d)
printf( "\n=============\nString b = >%s< and
is %d characters long\n", b, strlen( b ) );
/* put in a space and add the array a to what is in
array a */
strcat ( b, " " );
printf( "After strcat(b, \" \"), string b = >%s< and is
%d characters long\n", b, strlen( b ) );
strcat ( b, a );
printf( "After strcat(b, a), string b = >%s< and is
%d characters long\n", b, strlen( b ) );
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Sample Program (cont’d)
/* get the first token (delimited by a blank) */
printf( "strtok( b, \" \" ) gives %s\n", strtok( b, " " )
);
printf( "\n=============\n");
printf( "string a = %s string c = %s\n", a, c );
/* "Excellence" comes before "Failure", so print a
negative number */
printf( "strcmp( a, c ) gives %d\n", strcmp( a, c ) );
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Sample Program (cont’d)
/* " Failure " comes before “Excellence ", so print
a positive number */
printf( "strcmp( c, a ) gives %d\n", strcmp( c, a ) );
/* "Excellence" is the same as "Excellence", so
print zero */
printf( "strcmp( a, \"Excellence\" gives %d\n",
strcmp( a, "Excellence" ) );
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Sample Program (cont’d)
result = strcmp( "CMSC", "IFSM" ); /* negative
*/
printf( "After strcmp( \"CMSC\", \"IFSM\" ), result
is %d\n", result);
result = strcmp( "IFSM", "CMSC" ); /* positive */
printf( "After strcmp( \"IFSM\", \"CMSC\" ), result
is %d\n", result);
result = strcmp( "CMSC", "CMSC" ); /* zero */
printf( "After strcmp( \"CMSC\", \"CMSC\" ), result
is %d\n", result);
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Sample Program (cont’d)
printf( "\n=============\n");
/* convert a string to an integer */
printf( "atoi( \"1234\" gives %d\n", atoi( "1234" ) );
/* convert a string to a float */
printf( "atof( \"1234.5678\" ) gives %f\n", atof(
"1234.5678" ) );
return 0;
}
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Sample Program Output
string a is >Excellence<
After strcpy(b, a), string b is now >Excellence<
=============
String b = >Excellence< and is 10 characters long
After strcat(b, " "), string b = >Excellence < and is 11
characters long
After strcat(b, a), string b = >Excellence
Excellence< and is 21 characters long
strtok( b, " " ) gives Excellence
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Sample Program Output (cont’d)
=============
string a = Excellence string c = Failure
strcmp( a, c ) gives -1
strcmp( c, a ) gives 1
strcmp( a, "Excellence" gives 0
After strcmp( "CMSC", "IFSM" ), result is -1
After strcmp( "IFSM", "CMSC" ), result is 1
After strcmp( "CMSC", "CMSC" ), result is 0
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Sample Program Output (cont’d)
=============
atoi( "1234" gives 1234
atof( "1234.5678" ) gives 1234.567800
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