CSCI1190: Beginning C Programming for Engineers

1
CSCI-1190 Beginning C Programming for Engineers

• Lecture 5 Characters and Strings
• Gang Chen

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Characters

• Type char
• Characters are small integers (0-255)
• Character constants are integers that denote
  corresponding characters
• '0','1','A','B','a','b','\n'
• ASCII code maps characters to integers

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ASCII Code
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Strings

• Two interpretations
• Arrays whose elements are characters
• Pointers pointing to characters
• Strings are always terminated with a NULL
  character ('\0' or 0)
• char a"hello\n" / size? /
• char bhello\n

a0
a1
a2
a3
a4
a5
a6
b
(b1)
(b2)
(b3)
(b4)
(b5)
(b6)
o
l
l
e
h
\n
null
111
108
108
101
104
10
0
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Input/Output with Strings

• include ltstdio.hgt
• int main()
• char s10
• scanf("s",s) / bad /
• scanf("9s",s) / good /
• printf("s",s)
• return 0

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String Operations

• The header file string.h contains functions that
  work with strings
• strlen(a) number of characters in a
• strcmp(a,b) compares a and b, returning 0 if
  they are equal
• NOT ab
• strcpy(a,b) copies contents of b into a
• NOT ab

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In-Class Exercise 5-1

• Write a program that reads a line of text from
  the keyboard using the gets() funtion, then
  prints it out backwards. For instance, if you
  type in the line
• Test data
• The result should be
• atad tseT
• The syntax for the gets() function
• char s100
• gets(s)
• Make use of the strlen() function

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Converting Numeric Strings to Numbers

• From characters to digits
• / a is a character /
• na-'0' / n is now a digit /
• From digits to numbers
• 3492 2910410031000
• 210(910(4103))

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In-Class Exercise 5-2

• Write a program that reads an integer represented
  as a string from the keyboard, then coverts the
  string to the integer and prints it out.
• Notes
• You must use scanf("s",s) to read a string
• Do NOT use atoi() or any other similar functions