Chapter 10 Strings and Pointers

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Chapter 10 Strings and Pointers
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Introduction

• String Constant
• Example printf(Hello)
• Hello a string constant
• A string constant is a series of characters
  surrounded by double quotes.
• How to declare a variable to store string values?
• Represent a string using a one-dimensional array
  of type char
• char stringsize
• Question The size of a character array is fixed,
  how can this variable take string constants with
  different lengths as values?

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Outline

• String
• Representation of a string \0
• Using scanf to read in string
• Initilization of strings
• String-Handling Functions in the Standard Library
• Passing Arguments to main() using an array of
  strings

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The End-of-String Sentinel \0

• A string is
• a one-dimensional array of type char.
• char w100
• character value \0 is used to terminate a string
• strings have a variable length delimited by the
  null character \0 but with a maximum length
  determined by the size of the character array
• The size of the string must include the storage
  needed for the null character \0.

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The End-of-String Sentinel \0
the null character value \0 is used to terminate
a string

• Example

include ltstdio.hgt int main(void) char
w100 w0'A' w1'B'
w2'C' w3'\0' printf("s\n", w)
include ltstdio.hgt int main(void) char
w100 w0'A' w1'B'
w2'C' w3'\0' w4D'
printf("s\n", w)
a.out ABC
a.out ABC
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The End-of-String Sentinel \0
The size of the string must include the storage
needed for the null character \0.

• Example

include ltstdio.hgt int main(void) char
w3 w0'A' w1'B' w2'C'
w3'\0' printf("s\n", w)
overrun the bounds of w
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Outline

• String
• Representation of a string \0
• Using scanf to read in string
• Initilization of strings
• String-Handling Functions in the Standard Library
• Passing Arguments to main() using an array of
  strings

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Using scanf to reading string

• Using scanf to read in a string
• scanf(s, w)
• read in non-white space characters
• positions the input stream to an initial
  non-white space character
• read in non-white space characters
• The process stops when a white space character or
  EOF is encountered.
• a null character is placed in memory to end the
  string.

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Using scanf to reading string

• scanf(s,w)
• read in non-white space characters
• positions the input stream to an initial
  non-white space character
• read in non-white space characters
• The process stops when a white space character or
  EOF is encountered.
• a null character is placed in memory to end the
  string.

include ltstdio.hgt int main(void) char
w10 printf("Enter strings\n", w)
scanf("s", w) printf("s\n", w)
a.out Enter strings Hello Hello
a.out Enter strings Hello World Hello
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Outline

• String
• Representation of a string \0
• Using scanf to reading string
• Initilization of strings
• String-Handling Functions in the Standard Library
• Passing Arguments to main() using an array of
  strings

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Initialization of Strings

• Initialization of Strings
• Example initialize a string variable as abc
• char s a, b, c, \0
• char sabc

include ltstdio.hgt int main(void) char
w"abc" printf("d\n", sizeof(w))
a.out 4
The size of the string must include the storage
needed for the null character \0.
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Initialization of Strings

• A pointer to char can also be initialized with a
  constant string.
• A string constant is stored in memory by the
  compiler.
• the pointer is assigned the address of the
  constant string in memory.
• Example char p abc

include ltstdio.hgt int main(void) char
p"abc" printf("s\n",p)
a.out abc
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Initialization of Strings

• Difference between
• initializing an array with a constant string and
• initializing a pointer with a constant string

include ltstdio.hgt int main(void) char
s"abcdefg" char p"abcdefg"
printf("s\n",s) printf("s\n",p)
printf("d\n",sizeof(p)) printf("d\n",sizeof
(s))
a.out abcdefg abcdefg 4 8
4 bytes is used to represent a memory address
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Initialization of Strings

• Difference between
• initializing an array with a constant string
• the array contains the individual characters
  followed by the null character
• initializing a pointer with a constant string
• A string constant is stored in memory by the
  compiler.
• the pointer is assigned the address of the
  constant string in memory.

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Examples Process a string using array notation
with subscripts
include ltstdio.hgt int main(void) char c,
name100 int i printf("Enter a
Message\n") for (i0 (cgetchar())!'\n'
i) nameic namei'\0'
for (i0 namei!'\0' i)
if(isupper(namei))
nameitolower(namei) else
if(islower(namei))
nameitoupper(namei)
printf("\ns\n", name)
a.out Enter a Message Have a Good Day! hAVE
A gOOD dAY!
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Examples Process a string using pointer
include ltstdio.hgt int main(void) char c,
name100, p int i printf("Enter a
Message\n") for (i0 (cgetchar())!'\n'
i) nameic namei'\0'
for (pname p!'\0' p)
if(isupper(p)) ptolower(p)
else if(islower(p))
ptoupper(p) printf("\ns\n",
name)
a.out Enter a Message Have a Good Day! hAVE
A gOOD dAY!
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Examples Process a string using pointer
include ltstdio.hgt int main(void) char s
"Hello World" printf("s\n", s)
printf("s\n", s1) printf("s\n", s2)
a.out Hello World ello World llo World
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Outline

• String
• String-Handling Functions in the Standard Library
• Passing Arguments to main() using an array of
  strings

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String-Handling Functions in the Standard Library

• String-handling functions
• Function prototypes are provided by string.h
• include ltstring.hgt
• Functions
• Concatenate two strings strcat (s1, s2)
• Compare two strings int strcmp (s1, s2)
• Copy s2 to s1 strcpy (s1, s2)
• Length of a string strlen (s)

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String-Handling Functions in the Standard Library

• char strcat (char s1, const char s2)
• Concatenates s1 and s2, the result is put in s1.
  The string s1 is returned.

include ltstdio.hgt include ltstring.hgt int
main(void) char s1100 "Good Day" char
s2100 "Hello World" strcat(s1, s2)
printf("s2s, s1 s\n", s2, s1) strcat(s1,
s26) printf("s2s, s1 s\n", s2, s1)
a.out s2Hello World, s1 Good DayHello
World s2Hello World, s1 Good DayHello WorldWorld
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String-Handling Functions in the Standard Library

• int strcmp (const char s1, const char s2)
• An integer is returned that is less than, equal
  to, or greater tan zero, depending on whether s1
  is lexicographically less than, equal to, or
  greater than s2

include ltstdio.hgt include ltstring.hgt int
main(void) char s1100 "Good Day" char
s2100 "Hello World" printf("d\n",
strcmp(s1, s2)) printf("d\n", strcmp(s1,
s1)) printf("d\n", strcmp(s2, s1))
a.out -1 0 1
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String-Handling Functions in the Standard Library

• char strcpy (char s1, const char s2)
• s2 is copied into s1 until \0 is moved. Whatever
  exists in s1 is overwritten.
• It is assumed that s1 has enough space to hold
  the result.
• The value s1 is returned.

include ltstdio.hgt include ltstring.hgt int
main(void) char s1100 "Good Day" char
s2100 "Hello World" strcpy(s1, s2)
printf("s2s, s1 s\n", s2, s1)
strcpy(s11, s2) printf("s2s, s1 s\n",
s2, s1) strcpy(s11, s26) printf("s2s,
s1 s\n", s2, s1)
a.out s2Hello World, s1 Hello World s2Hello
World, s1 HHello World s2Hello World, s1 HWorld
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String-Handling Functions in the Standard Library

• unsigned strlen (const char s)
• A count of the number of characters before \0 is
  returned.

include ltstdio.hgt include ltstring.hgt int
main(void) char s1100 "Good Day"
printf("d\n", strlen(s1))
a.out 8
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Outline

• String
• String-Handling Functions in the Standard Library
• Passing Arguments to main() using an array of
  strings

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Passing Arguments to main()

• How main() communicates with the operating
  system?
• int main(void)
• int main( int argc, char argv)
• argc the number of the command line arguments
• argv an array of strings

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Passing Arguments to main()
include ltstdio.hgt int main(int argc, char
argv) int i printf("d \n", argc)
for (i0 i lt argc i) printf("s\n",
argvi)
a.out Hello World 3 a.out Hello World
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Summary

• String
• Representing a string using an array of
  characters
• \0 is used to terminated a string
• ? strings have a variable length delimited by the
  null character \0 but with a maximum length
  determined by the size of the character array
• initialization of strings
• String-Handling Functions in the Standard Library
• Passing Arguments to main()
• argc number of arguments
• argv an array of strings