METU Dept' of Computer Eng' Summer 2002

1
Lecture 08
Mon July 24, 2002

• METU Dept. of Computer Eng. Summer 2002
• Ceng230 - Section 01
• Introduction To C Programming
• by Ahmet Sacan

2
Copying Arrays

• an array cannot be directly assigned to another
  array.
• int x100, y100
• x y / ILLEGAL /
• You must copy values one-by-one
• for(i0 ilt100 i)
• xi yi

3
Perfect your skills at

• using arrays in loops, esp. in for-loops.
• for(i0 iltARR_SIZE i)
• scanf("d", arri)
• printf("d", arri)

4
Array Initialization

• int myscores3 90, 95, 56
• int ttt33 0,1,0, 2,0,0, 1,0,2
• int ttt33 0,1,0,2,0,0,1,0,0
• char myName5 'a', 'h', 'm', 'e', 't'

5
options...

• Can omit size when initializers are specified.
• int myScores 90, 95, 56
• when less initializers than the size, the rest
  filled with zeros. (?)
• int myScores3 90,95 /same as 90,95,0
  /
• int goals6 1,2,0 /same as 1,2,0,0,0,0
  /

6
character arrays

• a character array may be initialized using a
  double-quoted string.
• char myName6 "ahmet" / why 6? /
• char myName6 'a','h','m','e','t','\0'

7
errors...

• more initializers than size
• int scores3 90,100,50, 20
• accessing unallocated blocks
• int scores3 90,100,50
• ...
• scores4 3

8
Arrays as Arguments

• Write a function that takes in a float-array of
  size 10, and returns the average of these 10
  numbers.

9
Arrays as arguments

• float avg( float x10 )
• int i float sum 0
• for(i0 i lt 10 i)
• sum xi
• return sum/10
• void main()
• float arr10
• ...
• a avg( arr )
• ...

10
Goal

• Write a function that takes a float-array of any
  size, and returns the average of the elements.

11

• float avg( float x, int size )
• int i float sum 0
• for(i0 i lt size i)
• sum xi
• return sum/size
• void main()
• float arr10
• ...
• a avg( arr , 5)
• ...

12
when...

• ... array dimension is greater than 1, all but
  first dimension size must be specified.
• define MAXCOLS 5
• int PrintMatrix(int aMAXCOLS, int rows)

13
more on char

• we'll call a null ('\0') terminated character
  array a string.
• char mystr16 "hello"
• is equivalent to
• char mystr16 'h', 'e', 'l', 'l', 'o','\0'

14
char array initialization

• to initialize a character array, you can use a
  double-quoted string only when you are declaring
  the array.
• char lastName32 "sacan"
• lastName "ekmen" / INVALID /
• make sure that array is long enough to hold the
  string. Leave one extra character for '\0' - null
  character.
• char name6 "ahmet"

15
Printing char arrays

• Like regular arrays, you may use a for-loop to
  print individual elements
• Or, use s, so that printf takes care of it for
  you...
• printf("s", arr)

16
Goal

• Write a function that prints a character array,
  char-by-char.

17

• void PrintCharArr(char str , int maxSize)
• int i
• for(i0 iltsize i)
• if(stri '\0')
• break
• printf("c", arri)

18
Reading Input-Line into char-array

• Use the special function fgets, defined in
  stdio.h, to read a line of input.
• The fgets() function reads characters from the
  stream into the array pointed to by s, until n-1
  characters are read, or a newline character is
  read and transferred to s, or an end-of-file
  condition is encountered. The string is then
  terminated with a null character.
• fgets(str, MAX_SIZE, stdin)

19
Goal

• Read a line of input into an array and print the
  array character by character.

20

• define MAX_SIZE 256
• void main()
• int i
• char strMAX_SIZE
• printf("enter string ")
• fgets(str, MAX_SIZE, stdin)
• for(i0 iltMAX_SIZE i)
• if(stri '\0')
• break
• printf("c", stri)

sample Run enter string trshx trshx
21
Goal

• Write a function that takes a character-array as
  input, and its maximum size, and returns the
  length of the string contained in the array.

22

• int GetStrLength(char str , int maxLen)
• int i
• for(i0 iltmaxLen i)
• if(stri '\0')
• return i
• return 0 / not a null-terminated array /

23
Back to Non-char arrays.
24
Goal

• Write a function that takes does matrix
  production.
• Function takes three matrices and their sizes,
  put the product of the first two into the third.

25

• define MAXCOLS
• void MatProd(float x MAXCOLS, int xR,
  xC, float y MAXCOLS, yC, float z
  MAXCOLS, int zA, zB)
• int i,j,k
• for(i0 i lt xR i)
• for(j0 j lt xC j)
• zij 0
• for(k0 k lt yC k)
• zij xik ykj