Arrays in C++: Numeric Character (Part 2). Passing Arrays as Arguments in C++, arrays are always...
-
Upload
sharlene-welch -
Category
Documents
-
view
236 -
download
3
Transcript of Arrays in C++: Numeric Character (Part 2). Passing Arrays as Arguments in C++, arrays are always...
![Page 1: Arrays in C++: Numeric Character (Part 2). Passing Arrays as Arguments in C++, arrays are always passed by reference (Pointer) whenever an array is passed.](https://reader036.fdocuments.in/reader036/viewer/2022062320/56649f455503460f94c6649d/html5/thumbnails/1.jpg)
Arrays in C++:
NumericCharacter(Part 2)
![Page 2: Arrays in C++: Numeric Character (Part 2). Passing Arrays as Arguments in C++, arrays are always passed by reference (Pointer) whenever an array is passed.](https://reader036.fdocuments.in/reader036/viewer/2022062320/56649f455503460f94c6649d/html5/thumbnails/2.jpg)
Passing Arrays as Arguments
in C++, arrays are always passed by reference (Pointer)
whenever an array is passed as an argument, its base address is sent to the called function
![Page 3: Arrays in C++: Numeric Character (Part 2). Passing Arrays as Arguments in C++, arrays are always passed by reference (Pointer) whenever an array is passed.](https://reader036.fdocuments.in/reader036/viewer/2022062320/56649f455503460f94c6649d/html5/thumbnails/3.jpg)
Using Arrays as Arguments to Functions
Generally, functions that work with arrays require 2 items of information as arguments:
the beginning memory address of the array (base address)
the number of elements to process in the array
![Page 4: Arrays in C++: Numeric Character (Part 2). Passing Arrays as Arguments in C++, arrays are always passed by reference (Pointer) whenever an array is passed.](https://reader036.fdocuments.in/reader036/viewer/2022062320/56649f455503460f94c6649d/html5/thumbnails/4.jpg)
Simple Exampleconst int MAX=5;float get_sum(float vector[]); // Prototypeint main ( )
{ float sum, scores[MAX];
<assign values to scores>sum = get_sum(scores);return 0;
}float get_sum (float vector[]) // definition{ float total = 0.0;
int j; for (j = 0; j < MAX; ++j)
total += vector[j];return total;
}
![Page 5: Arrays in C++: Numeric Character (Part 2). Passing Arrays as Arguments in C++, arrays are always passed by reference (Pointer) whenever an array is passed.](https://reader036.fdocuments.in/reader036/viewer/2022062320/56649f455503460f94c6649d/html5/thumbnails/5.jpg)
Programming Tip
When passing an array as an argument, also pass the size of the array.Previous example revisited
![Page 6: Arrays in C++: Numeric Character (Part 2). Passing Arrays as Arguments in C++, arrays are always passed by reference (Pointer) whenever an array is passed.](https://reader036.fdocuments.in/reader036/viewer/2022062320/56649f455503460f94c6649d/html5/thumbnails/6.jpg)
Question
How to pass an element or part of an array as a parameter?
-- Revisit the previous example
![Page 7: Arrays in C++: Numeric Character (Part 2). Passing Arrays as Arguments in C++, arrays are always passed by reference (Pointer) whenever an array is passed.](https://reader036.fdocuments.in/reader036/viewer/2022062320/56649f455503460f94c6649d/html5/thumbnails/7.jpg)
#include <iostream>#include <iomanip>using namespace std;
void obtain ( int [ ], int ) ; // prototypes here void findWarmest ( const int[ ], int , int& ) ; // note const here void findAverage ( const int[ ], int , int& ) ;void print ( const int [ ], int ) ;
int main ( ){ int temp[31] ; // array to hold up to 31 temperatures int numDays ; int average=0 ; int hottest =0; int m ;
Example with Array Parameters
![Page 8: Arrays in C++: Numeric Character (Part 2). Passing Arrays as Arguments in C++, arrays are always passed by reference (Pointer) whenever an array is passed.](https://reader036.fdocuments.in/reader036/viewer/2022062320/56649f455503460f94c6649d/html5/thumbnails/8.jpg)
cout << “How many daily temperatures? ”; cin >> numDays;
obtain( temp, numDays ) ; // call passes value of numDays and // address of array temp to function
cout << numDays << “ temperatures“; print ( temp, numDays ) ;
findAverage ( temp, numDays, average ) ; findWarmest ( temp, numDays, hottest ) ;
cout << “Average was: “ << average << endl; cout << “Highest was: “ << hottest << endl; return 0;}
![Page 9: Arrays in C++: Numeric Character (Part 2). Passing Arrays as Arguments in C++, arrays are always passed by reference (Pointer) whenever an array is passed.](https://reader036.fdocuments.in/reader036/viewer/2022062320/56649f455503460f94c6649d/html5/thumbnails/9.jpg)
Memory Allocated for Array
temp[0] temp[1] temp[2] temp[3] temp[4] . . . . . temp[30]
6000
Base Address
50 65 70 62 68 ..
int temp[31] ; // array to hold up to 31 temperatures
![Page 10: Arrays in C++: Numeric Character (Part 2). Passing Arrays as Arguments in C++, arrays are always passed by reference (Pointer) whenever an array is passed.](https://reader036.fdocuments.in/reader036/viewer/2022062320/56649f455503460f94c6649d/html5/thumbnails/10.jpg)
void obtain ( /* out */ int temp [ ] , /* in */ int number )
/* Has user enter number temperature values at keyboard
// Precondition:// number is assigned && number > 0// Postcondition:// temp [ 0 . . number -1 ] are assigned */{ int m;
for ( m = 0 ; m < number; m++ ) { cout << “Enter a temperature : “; cin >> temp [m]; }}
![Page 11: Arrays in C++: Numeric Character (Part 2). Passing Arrays as Arguments in C++, arrays are always passed by reference (Pointer) whenever an array is passed.](https://reader036.fdocuments.in/reader036/viewer/2022062320/56649f455503460f94c6649d/html5/thumbnails/11.jpg)
void print ( /* in */ const int temp [ ] , /* in */ int number )
/* Prints number temperature values to screen// Precondition:// number is assigned && number > 0// temp [0 . . number -1 ] are assigned// Postcondition:// temp [ 0 . . number -1 ] have been printed 5 to a line*/{
int m; cout << “You entered: “; for ( m = 0 ; m < number; m++ ) { if ( m % 5 == 0 ) cout << endl; cout << setw(7) << temp [m]; }}
![Page 12: Arrays in C++: Numeric Character (Part 2). Passing Arrays as Arguments in C++, arrays are always passed by reference (Pointer) whenever an array is passed.](https://reader036.fdocuments.in/reader036/viewer/2022062320/56649f455503460f94c6649d/html5/thumbnails/12.jpg)
Use of const
because the identifier of an array holds the base address of the array, an & is never needed for an array in the parameter list
arrays are always passed by reference
to prevent elements of an array used as an argument from being unintentionally changed by the function, you place const in the function heading and prototype
![Page 13: Arrays in C++: Numeric Character (Part 2). Passing Arrays as Arguments in C++, arrays are always passed by reference (Pointer) whenever an array is passed.](https://reader036.fdocuments.in/reader036/viewer/2022062320/56649f455503460f94c6649d/html5/thumbnails/13.jpg)
Use of const in prototypes
void obtain ( int [ ], int ) ;
void findWarmest ( const int [ ], int, int& ) ;
void findAverage ( const int [ ], int, int& ) ;
void print ( const int [ ], int ) ;
do not use const with outgoing array becausefunction is supposed to change array values
use const with incoming array values to prevent unintentional changes by function
![Page 14: Arrays in C++: Numeric Character (Part 2). Passing Arrays as Arguments in C++, arrays are always passed by reference (Pointer) whenever an array is passed.](https://reader036.fdocuments.in/reader036/viewer/2022062320/56649f455503460f94c6649d/html5/thumbnails/14.jpg)
void findAverage ( /* in */ const int temp [ ] , /* in */ int number , /* out */ int& avg )
/* Determines average of temp[0 . . number-1]// Precondition:// number is assigned && number > 0// temp [0 . . number -1 ] are assigned// Postcondition:// avg = arithmetic average of temp[0 . . number-1]*/{
int m; int total = 0; for ( m = 0 ; m < number; m++ ) { total = total + temp [m] ; }
avg = int (float (total) / float (number));}
![Page 15: Arrays in C++: Numeric Character (Part 2). Passing Arrays as Arguments in C++, arrays are always passed by reference (Pointer) whenever an array is passed.](https://reader036.fdocuments.in/reader036/viewer/2022062320/56649f455503460f94c6649d/html5/thumbnails/15.jpg)
void findWarmest ( /* in */ const int temp [ ] , /* in */ int number , /* out */ int& largest )
/* Determines largest of temp[0 . . number-1]// Precondition:// number is assigned && number > 0// temp [0 . . number -1 ] are assigned// Postcondition:// largest=largest value in temp[0 . . number-1] */{
int m; largest = temp[0] ; // initialize largest to first element
// then compare with other elements
for ( m = 0 ; m < number; m++ ) { if ( temp [m] > largest ) largest = temp[m] ; }}
![Page 16: Arrays in C++: Numeric Character (Part 2). Passing Arrays as Arguments in C++, arrays are always passed by reference (Pointer) whenever an array is passed.](https://reader036.fdocuments.in/reader036/viewer/2022062320/56649f455503460f94c6649d/html5/thumbnails/16.jpg)
Using arrays for Counters
Write a program to count the number of each alphabet letter in a text file.
letterASCII
‘A’ 65
‘B’ 66
‘C’ 67
‘D’ 68 . . . . . .
‘Z’ 90
This is my text file.
It contains many
things!
5 + 8 is not 14.
Is it?
“my.dat”
![Page 17: Arrays in C++: Numeric Character (Part 2). Passing Arrays as Arguments in C++, arrays are always passed by reference (Pointer) whenever an array is passed.](https://reader036.fdocuments.in/reader036/viewer/2022062320/56649f455503460f94c6649d/html5/thumbnails/17.jpg)
const int SIZE 91;int freqCount[SIZE]={0};
freqCount [ 0 ] 0
freqCount [ 1] 0 . . . . . .freqCount [ 65 ] 2
freqCount [ 66 ] 0 . . . . . .
freqCount [ 89] 1
freqCount [ 90 ] 0
unused
counts ‘A’ and ‘a’
counts ‘B’ and ‘b’ . . .
counts ‘ Y’ and ‘y’
counts ‘Z’ and ‘z’
![Page 18: Arrays in C++: Numeric Character (Part 2). Passing Arrays as Arguments in C++, arrays are always passed by reference (Pointer) whenever an array is passed.](https://reader036.fdocuments.in/reader036/viewer/2022062320/56649f455503460f94c6649d/html5/thumbnails/18.jpg)
Main Module Pseudocode
Level 0Open dataFile (and verify success)Zero out freqCountRead ch from dataFileWHILE NOT EOF on dataFile
If ch is alphabetic characterIf ch is lowercase alphabetic
Change ch to uppercaseIncrement freqCount[ch] by 1
Read ch from dataFilePrint characters and frequencies
![Page 19: Arrays in C++: Numeric Character (Part 2). Passing Arrays as Arguments in C++, arrays are always passed by reference (Pointer) whenever an array is passed.](https://reader036.fdocuments.in/reader036/viewer/2022062320/56649f455503460f94c6649d/html5/thumbnails/19.jpg)
/* Program counts frequency of each alphabetic character in text file. */
#include <iostream>#include <ifstream>#include <cstdlib>#include <ctype>using namespace std;
const int SIZE 91;void printOccurrences ( const int [ ] ) ; /*prototype */
Counting Frequency of Alphabetic Characters
![Page 20: Arrays in C++: Numeric Character (Part 2). Passing Arrays as Arguments in C++, arrays are always passed by reference (Pointer) whenever an array is passed.](https://reader036.fdocuments.in/reader036/viewer/2022062320/56649f455503460f94c6649d/html5/thumbnails/20.jpg)
int main ( ){
ifstream inStream; int freqCount [SIZE ]; char ch , index;
inStream.open(“my.dat”) ; /* open and verify success */ if ( inStream.fail()) { cout << “ CAN’T OPEN INPUT FILE ! “; exit(1); } for ( int m = 0 ; m < SIZE ; m++ ) /* zero out the array */
freqCount [ m ] = 0 ;
![Page 21: Arrays in C++: Numeric Character (Part 2). Passing Arrays as Arguments in C++, arrays are always passed by reference (Pointer) whenever an array is passed.](https://reader036.fdocuments.in/reader036/viewer/2022062320/56649f455503460f94c6649d/html5/thumbnails/21.jpg)
inStream.get(ch); /* read file one character at a time */ while ( ! inStream.eof( ) ) /* while last read was successful */ {
if (isalpha ( ch ) ){
if ( islower ( ch ) )ch = toupper ( ch ) ;
freqCount [ ch ] = freqCount [ ch ] + 1 ;/* use ch as a type of integer*/
}inStream.get(ch); /* get next character */
}printOccurrences ( freqCount ) ;return 0;
} // end of main function
![Page 22: Arrays in C++: Numeric Character (Part 2). Passing Arrays as Arguments in C++, arrays are always passed by reference (Pointer) whenever an array is passed.](https://reader036.fdocuments.in/reader036/viewer/2022062320/56649f455503460f94c6649d/html5/thumbnails/22.jpg)
void printOccurrences ( const int freqCount [ ] )
// Prints each alphabet character and its frequency
// Precondition:
// freqCount [ ‘A’ . . ‘Z’ ] are assigned
// Postcondition:
// freqCount [ ‘A’ . . ‘Z’ ] have been printed */
{ char index ;
cout << “File contained\n “;
cout << “LETTER OCCURRENCES\n”;
for ( index = ‘A’ ; index < = ‘Z’ ; index++ )
{
cout << index <<“\t”
<< freqCount [ index ] << endl;
}
}
![Page 23: Arrays in C++: Numeric Character (Part 2). Passing Arrays as Arguments in C++, arrays are always passed by reference (Pointer) whenever an array is passed.](https://reader036.fdocuments.in/reader036/viewer/2022062320/56649f455503460f94c6649d/html5/thumbnails/23.jpg)
More about Array Index
array index can be any integral type. This includes char and enum type.
it is programmer’s responsibility to make sure that an array index does not go out of bounds. The index must be within the range 0 through the declared array size minus one
using an index value outside this range causes the program to access memory locations outside the array. The index value determines which memory location is used