Lecture 21:Arrays and Strings(cont.)

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Lecture 21Arrays and Strings(cont.)

• Introduction to Computer Science
• Spring 2006

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Arrays

• Array - a collection of a fixed number of
  elements
• All the elements of an array must be the same
  data type
• The elements of an array are stored sequentially
  in memory.
• One-dimensional array - an array in which the
  components are arranged in a list form
• The syntax for declaring a one-dimensional array
  is
• dataType arrayNameintExp
• where intExp is any expression that
  evaluates to a positive integer
• Example int num5

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include ltiostreamgt include ltiomanipgt using
namespace std const int arraySize 10 void
fill_Array(double list, int listSize)
for(int i0 iltlistSize i)
cingtgtlisti void print_Array(double list,
int listSize) for(int i0 iltlistSize i)
coutltltsetw(5)ltltlisti void
copy_Array(const double listOne, double
listTwo, int listOneSize) for(int i0
iltlistOneSize i) listTwoi
listOnei void square_Array(double list,
int listSize) int k for (int i 0 i lt
listSize i) k i 1 / i runs from 0
to 9 / / k runs from 1 to 10 / listi
kk cout ltlt "The square of " ltlt k ltlt " is " ltlt
listi ltlt endl int main() double
listAarraySize0 double listBarraySize
fill_Array(listA, arraySize) print_Array(listA,
arraySize) copy_Array(listA, listB,
arraySize) square_Array(listA, arraySize)
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Two-Dimensional Arrays

• Two-dimensional Array a collection of a fixed
  number of components arranged in two dimensions
• The syntax for declaring a two-dimensional array
  is
• dataType arrayNameintexp1intexp2
• where intexp1 and intexp2 are expressions
  yielding positive integer values
• The two expressions intexp1 and intexp2 specify
  the number of rows and the number of columns,
  respectively, in the array
• Two-dimensional arrays are sometimes called
  matrixes or tables
• Two-dimensional arrays are stored in row order
• The first row is stored first, followed by the
  second row, followed by the third row and so on

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Two-Dimensional Arrays(cont.)

• Example double sales105

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Accessing Array Components

• The syntax to access a component of a
  two-dimensional array is
• arrayNameindexexp1indexexp2
• where indexexp1 and indexexp2 are expressions
  yielding nonnegative integer values
• indexexp1 specifies the row position and
  indexexp2 specifies the column position
• Example sales5325.75

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Accessing Array Components

• A common way to access the elements of a
  two-dimensional arrays is with nested for
  loops.const int MAXI 50const int MAXJ
  75int main()
• int i int j float valuesMAXIMAXJ for
  (i 0 i lt MAXI i)     for (j 0 j lt
  MAXJ j)         valuesij
  whatever     

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Initialization

• Like one-dimensional arrays
• Two-dimensional arrays can be initialized when
  they are declared
• Example
• int board43 2, 3, 1,
• 15, 25, 13,
• 20, 4, 7,
• 11, 18, 14

• To initialize a two-dimensional array when it is
  declared
• Elements of each row are enclosed within braces
  and separated by commas
• All rows are enclosed within braces
• For number arrays, if all components of a row
  are not specified, the unspecified components are
  initialized to zero

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Processing Two-Dimensional Arrays

• A two-dimensional array can be processed in three
  different ways
• Process the entire array
• Process a particular row of the array, called row
  processing
• Process a particular column of the array, called
  column processing

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Processing Two-Dimensional Arrays Row
processing and Column processing

• We can process a particular row or column of a
  two-dimensional array as a one-dimensional array
• use algorithms similar to processing
  one-dimensional arrays
• For example
• the following for loop initializes row four to
  zero
• row 4
• for(col 0 col lt columns col)
• matrixrowcol 0
• The following for loop inputs data in row 4 of
  matrix
• row 4
• for(col 0 col lt columns col)
• cingtgtmatrixrowcol

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Processing Two-Dimensional Arrays Entire Array

• We can process the entire array by using nested
  for loop
• Example
• The following nested for loop initialize the
  entire matrix
• for(row 0 row lt rows row)
• for(col 0 col lt columns col)
• matrixrowcol 0

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Print

• The following nested for loops print the
  components of matrix, one row per line
• for(row 0 row lt rows row)
• for(col 0 col lt columns col)
• coutltltsetw(5)ltltmatrixrowcolltlt" "
• coutltltendl

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Input

• The following nested loop input data in each
  component of the matrix
• for(row 0 row lt rows row)
• for(col 0 col lt columns col)
• cingtgtmatrixrowcol

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Passing Two-Dimensional Arrays as Parameters to
Functions

• Two-dimensional arrays can be passed as
  parameters to a function
• By default, arrays are passed by reference
• The base address, that is, the address of the
  first component of the actual parameter is passed
  to the formal parameter
• When declaring a two-dimensional array as a
  formal parameter
• Can omit size of first dimension, but not the
  second
• Number of columns must be specified

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include ltiostreamgt include ltiomanipgt using
namespace std const int MAXI 10 const int
MAXJ 15 void init_matrix(double
matrixMAXIMAXJ) for(int i0 iltMAXI
i) for(int j0 jltMAXJ
j) matrixijij void
print_matrix(double matrixMAXIMAXJ) for(int
i0 iltMAXI i) for(int
j0 jltMAXJ j) coutltltsetw(5)ltltmatrixij
coutltltendl double
sum_matrix(double matrixMAXIMAXJ) double
sum0.0 for(int i0 iltMAXI i)
for(int j0 jltMAXJ j) sum sum
matrixij return sum int
main() double matrixMAXIMAXJ double
sum init_matrix(matrix) print_matrix(matrix)
sum sum_matrix(matrix) coutltlt"The sum of
all the elements of matrix is "ltltsumltltendl
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End of lecture 21

• Thank you!