1. Characters and Strings
Department of Computer and Information Science, School of Science, IUPUI
CSCI N305
Characters and Strings
Literals and Variables

2. Fundamentals of Strings and Characters
Building blocks of programs
Every program is a sequence of meaningfully grouped characters
Character constant
An int value represented as a character in single quotes
'z' represents the integer value of z
Strings
Series of characters treated as a single unit
Can include letters, digits and special characters (*, /, $)
String literal (string constant) - written in double quotes
"Hello"
Strings are arrays of characters
String a pointer to first character
Value of string is the address of first character

3. Fundamentals of Strings and Characters
String declarations
Declare as a character array or a variable of type char *
char color[] = "blue";
char *colorPtr = "blue";
Remember that strings represented as character arrays end with '\0'
color has 5 elements
Inputting strings
Use scanf
scanf("%s", word);
Copies input into word[]
Do not need & (because a string is a pointer)
Remember to leave room in the array for '\0'

4. Character Pointers String constant acts like a character pointer
char *pc = “ABCDE”; /* declare a character pointer variable */
Variable Address Value
constant ‘A’
constant ‘B’
constant ‘C’
constant ‘D’
constant ‘E’
constant ‘\0’ pc
char s1[] = “abc”;
s1[0] ‘a’
s1[1] ‘b’
s1[2] ‘c’
s1[3] ‘\0’
‘A’
‘B’
‘C’
‘D’
‘E’
‘\0’
731
732
733
734
735
736
800

5. Character Pointers Example: s2 s1[] s3[] s char s1[] = “abc”;
CONSTANT MEMORY AREA (READ ONLY)
Example:
char s1[] = “abc”;
char *s2 = “abc”;
f() {
s1[1] = ‘y’; /* OK */
s2[1] = ‘y’; /* wrong (PC is OK)*/
s1 = “test”; /* wrong */
s2 = “test”; /* OK */ }
char s3[] = “abcdef”;
f1()
char *s = s3;
*s = ‘A’; /* s3[0]=‘A’ */
s = “test”;
printf(“%s\n%s\n”,s,s2); s2
800
1100
100
100
‘a’
s1[]
1000
1001
1002
1003
‘a’
‘b’
‘c’
‘\0’
101
‘b’
102
‘c’
103
‘\0’
104
105
106
107
‘t’
‘e’
‘s’
‘\0’
108
1100
s3[]
2000 s
2001
2002
2003
‘a’
‘b’
‘c’
‘d’
2004
‘e’
s3[0]=‘A’
2000
2001
2002
2003
‘a’
‘b’
‘c’
‘d’
2004
‘e’
...

6. Pointer Arrays Syntax: int *pi[3]; float *pf[3]; int i=1, j=2, k=3;
/* pi[0], pi[1], pi[2] */
float *pf[3];
/* pf[0], pf[1], pf[2] */
Example 1:
int i=1, j=2, k=3;
int *pi[3] = {&i, &j, &k};
Example 2:
char *pc[3]={“ABC”, “DEF”, “GH”};
Variable
Address
Value
constant 90 ‘A’
constant 91 ‘B’
constant 92 ‘C’
constant 93 ‘\0’
constant 94 ‘D’
constant 95 ‘E’
constant 96 ‘F’
constant 97 ‘\0’
constant 98 ‘G’
constant 99 ‘H’
Constant ‘\0’
pc[0]
pc[1]
pc[2]
Variable
Address
Value i 80 1 j 82 2 k 84 3
pi[0]
100
pi[1]
101
pi[2]
102
Const
can not be
changed

7. Command-Line Arguments
argc and argv
In environments those support C, there is a way to pass command-line arguments or parameters to a program when it begin executing.
When main is called to begin execution, it is called with two arguments – argc and argv
argc : The first (conventionally called argc) is the number of command-line arguments the program was invoked with
argv : The second (conventionally called argv) is a pointer to an array of character strings that contain the arguments, one per string.
Example:
if echo is a program and executed on unix prompt, such as
10 <user:/home/droberts> echo hello world
pointer array
argv
argc
e c h o \0
h e l l o \0
w o r l d \0
null 3

8. Command-Line Arguments
Example: print out the arguments. ex: hello world
main (int argc, char *argv[]) {
int i;
for (i = 1; i < argc; i++)
printf(“%s%c”, argv[i], (i < argc-1) ? ‘ ’ : ‘\n’); }
while (--argc > 0)
printf(“%s%c”, *++argv, (argc > 1) ? ‘ ’ : ‘\n’);
printf((argc > 1) ? “%s “ ; “%s\n“, *++argv);