1. Lec 11

2. What’s a String ?
A string is a data structure that deals with the grouping of
characters.
In C, strings are implemented using arrays of type char.

3. Declaring and Initializing Strings
Declaration
char str_var[20]; /*declaring a string variable called str_var */
Initialization
char str_var[20]={'A', 'p', 'p', 'l', 'e', ' ', 'a', 'n', 'd', ' ', 'P', 'e', 'a', 'r', 's'};
char str_var[20]="Apples and Pears";

4. Single and Double Quotes
Single quotations are used to assign a character to a variable.
Example: if s is declared as char s; then the assignment statement
for s is s=‘L’;
Double quotations are used to assign a string to a variable.
Example: if s is declared as char s[10]; then the assignment
statement for s is s="Computers";

5. Arrays of Strings
Arrays of Strings is a two-dimensional array containing one
character in each element.
Example:
char months[12][10]=
{"January", "February", "March", "April", "May", "June",
"July", "August", "September", "October", "November",
"December"};
char names[4][6]={"Sara", "Nora", "Nada", "Moudy"};

6. Definitions Null character
The null character is represented by the character '\0'. This
character marks the end of the string in C.
White space characters
Blanks (space bar), new lines (enter), and tabs.
The %s placeholder
Used in scanf’s and printf’s to print a string.

7. Initializers and Strings
If number of initializers are less than the number of elements, the
null character is added after the last character.
char str_var[20]="Apples and Pears";
If number of initilaizers is more than the number of elements, a
compiler error occurs.
char x[4]="Hello";
If number of initilaizers equals the number of elements, a compiler
overflow error occurs.
char x[7]="Hangman";

8. scanf’s and Strings C o m p u t e r s \0 x scanf("%s", &x); /* word */
gets(x); /* word or sentince */
for (i=0; i<9; i++)
scanf("%c", &x[i]);
x[9]='\0';
Because the user cannot enter a null in a loop

9. scanf’s and Strings
When scanf encounters whitespace characters before the string it
skips these characters.
When scanf encounters whitespace characters after the string it stops
scanning and the null charcter is placed at the end.

10. printf’s and Strings C o m p u t e r s \0 x for (i=0; i<9; i++)
printf("%c", x[i]); or
for (i=0; x[i]!='\0'; i++)
printf(" %c", x[i]);
printf("%s", x);

11. Right and Left Justification
Char x[7] = "Hello!";
Left Justification
printf("%-20s", x);
Right Justification
printf("%20s", x);
Hello!
Hello!

12. String Manipulation Functions
strcpy(x,y);
strcpy: Makes a copy of the second argument into the first
argument. It automatically adds the null to the end of the first
argument.
Examples:
strcpy(x, "Hi");
strcpy(z, x);
destination
Source

13. String Manipulation Functions
strncpy(x,y,n);
strncpy: Makes a copy of up to n characters from the second
argument to the first. It does not add the null. It can be added
manually.
Examples:
strncpy(x, "Hi", 1);
strncpy(z, x, 1);

14. Example /* a program to demonstrate string assignments */
#include<stdio.h>
#include<string.h>
int main(void)
{char x[]="Happy Birthday to You";
char y[25], z[15];
printf("The string in array x is: %s\n", x);
strcpy(y,x);
printf("The string in array y is: %s\n", y);
strncpy(z, y, 14);
z[14]='\0';
printf("The string in array z is: %s\n", z);
return(0);}

15. Example /* a program that divides a string into substrings */
#include<stdio.h>
#include<string.h>
int main(void)
{char last[20], first[20], middle[20];
char name[20]="Lama Bandar Fahad";
strncpy(first, name, 4);
first[4]='\0';
strncpy(middle, &name[5], 6);
middle[6]='\0';
strcpy(last, &name[12]);
printf("%s %s %s\n", last, first, middle);
return(0);}

16. String Manipulation Functions
strlen(x);
strlen: Returns an integer number representing the number of
characters in a string not including the null character.
Examples:
i=strlen("Hi");
printf("%i", strlen("Hello"));

17. String Manipulation Functions
strcat(x,y);
strcat: Adds the string in the second argument to the end of the first.
Examples:
strcat(x, "!");

18. String Manipulation Functions
strncat(x,y,n);
strncat: Adds n characters of the string in the second argument to
the end of the first one.
Examples:
strncat(x, "the end", 3);

19. String Manipulation Functions
strcmp(x,y);
strcmp: compares x and y.
It returns a:
0 if x is equal to y.
1 if x is grater than y.
-1 if x is less than y.
Examples:
#include<stdio.h>
#include<string.h>
int main(void)
{char x[20]="universe";
char y[20]="university";
printf("%i\n", strcmp(x, y));
return(0);}

20. String Manipulation Functions
Summary:
strcpy(x,y); /* string assignment */
strncpy(x,y,n);
strlen(x); /* determining string length */
strcat(x,y); /* appending to a string */
strncat(x,y,n);
strcmp(x,y) /* comparing two strings */

21. Review (String Manipulation Functions)
char x[10]="The", y[5]="End!";
int n=3;
strcpy(x,y)
strncpy(x,y,n)
strlen(x)
strcat(x,y)
strncat(x,y,n)
strcmp(x,y)
x = "End!"
x = "End" 3
x = "TheEnd!"
x = "TheEnd" 1