1. ECE 103 Engineering Programming Chapter 25 C Strings, Part 1
Herbert G. Mayer, PSU CS
Status 7/24/2014
Initial content copied verbatim from
ECE 103 material developed by
Professor Phillip PSU ECE

2. Syllabus
String Data
Simple String Operations
Examples

3. String Data C lacks the built-in type string
Strings are approximated in C via arrays of characters
Declaration:
char stringname[ SIZE ];
Characters in the string occupy consecutive elements in the array 2

4. The first '\0' (null) character found in the array marks the end of the string. It must be present
When declaring a string, the array size must be big enough to hold both the string and '\0’
Declaring a character array larger than the expected string length allows the array to accommodate a larger string at a later time 3

5. Example: // Declare two strings char str1[ 4 ]; char str2[ 10 ];
// Initialize string one char at a time
str1[0]= 'C'; str1[1]= 'a'; str1[2]= 't';
str1[3]= '\0';
// Use up only 5 out of 10 elements
str2[0]= 'J'; str2[1]= 'a'; str2[2]= 'n'; str2[3]= 'e'; str2[4]= '\0'; 4

6. A literal string automatically has a '\0' at the end of the string
A literal string constant is delimited by double quotation marks (e.g., "Hello, world!”)
A literal string automatically has a '\0' at the end of the string
A string variable can be declared and initialized with a literal string constant
Example: char s[10] = "Hi, Bob!";
char mystr[] = " Good night everybody! ”;
char t1[4] = "Jim"; // OK
char t2[3] = "Jim"; // ERROR! Overflow 5

7. Example: char s[10] = "Hi, Bob!";
','
' '
'B'
'o'
'b'
'!'
'\0'
s[0]
'H'
1218
s[1]
'i'
1219
s[2]
','
1220
s[3]
' '
1221
s[4]
'B'
1222
s[5]
'o'
1223
s[6]
'b'
1224
s[7]
'!'
1225
s[8]
'\0'
1226
s[9]
1227
s is the address of the first character in the string.
s[j] is the j-th character in the string.
s is equivalent to &s[0].
Declared array size = 10
Valid array index range = 0 to 9
Space needed to store string = 9
Valid string index range = 0 to 8
String length = 8 6

8. What happens if we do this: s[6] = '\0'; ?
Example:
char s[10] = "Hi, Bob!";
What happens if we do this: s[6] = '\0'; ?
The string stored in s is now “Hi, Bo” instead of “Hi, Bob!”
s[0]
s[1]
s[2]
s[3]
s[4]
s[5]
s[6]
s[7]
s[8]
s[9]
s →
'H'
'i'
','
' '
'B'
'o'
'b'
'!'
'\0'
s[0]
s[1]
s[2]
s[3]
s[4]
s[5]
s[6]
s[7]
s[8]
s[9]
s →
'H'
'i'
','
' '
'B'
'o'
'\0'
'!' 7

9. To embed a quotation mark in a string, use \" Example:
char str1[]="Hello"; /* Hello */
char str2[]="\"Hello\""; /* "Hello" */
To embed a backslash in a string, use \\
char winpath[]="C:\\windows"; /* C:\windows */ 8

10. Examples of Simple String Operations
Assume these string declarations:
char str1[ MAXSIZE ], str2[ MAXSIZE ];
Input a string (requires stdio.h)
fgets( str1, MAXSIZE, stdin );
Print a string
printf( "str1 = %s\n", str1 );
Copy a string (requires string.h)
strcpy( str1, "Hello” );
strcpy( str2, str1 );
Stores input in str1.
Copies “Hello” to str1.
Copies contents of str1 to str2. 9

11. Example: /* Simple string operations demonstration */
#include <stdio.h>
#include <string.h>
#define MAXLEN 100
int main( void )
{ // main
char str1[ MAXLEN ], str2[ MAXLEN ];
printf( "What is your name? ” );
fgets( str1, MAXLEN, stdin );
printf( "Hello, %s!\n", str1 );
return 0;
} //end main
Output:
What is your name? Joe
Hello, Joe !
Why does the exclamation point show up on a separate line?
fgets() stores the newline ('\n') that you typed as part of the string itself. 10