paul i lin 1 ecet 264 c programming with applications lecture 11 c arrays and applications paul i....

Paul I Lin 1

ECET 264 C Programming with

Applications

Lecture 11

C Arrays and Applications Paul I. Lin

Professor of Electrical & Computer Engineering Technology

http://www.etcs.ipfw.edu/~lin

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Lecture 11 – Array Applications

Determine Size of Arrays Passing Arrays to Functions Searching Arrays Multiple Subscripted Arrays Programming Applications

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Determining the Sizes and Bounds of

Arrays Array size Must be determined at design time Array boundary must be checked at run-

time sizeof operatorExamples

Determine the size of LCD array• sizeof(display_LCD)/sizeof(char)

Determine the size of data array• sizeof(data)/sizeof(int)

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Example 11 - 1

/* while0.c - Accessing data arrays using a while() loop and describe out of boundary*/

#include <stdio.h>// define format string#define FORMAT "data[%d] = %d,\ d[%d] = %d\n", i,data[i],i,d[i]

#define N 6static int data[] = { 1,2,3,4,5,6 }; // static array

definitionvoid main(){ int d[N], i, j, k; i = 0; j = 1; k = 2;

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while(i < N) {

d[i] = data[i] * 2; printf(FORMAT); i++;

}

/* Try access the array outside its boundary */ printf(FORMAT); // printf("data[%d] = %d,\ d[%d] = %d\n", i,data[i],i,d[i]) i++; printf(FORMAT);}

Example 11 – 1 (continue)

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Output:

data[0] = 1, d[0] = 2

data[1] = 2, d[1] = 4

data[2] = 3, d[2] = 6

data[3] = 4, d[3] = 8

data[4] = 5, d[4] = 10

data[5] = 6, d[5] = 12

data[6] = 1635017060, d[6] = 6618680

data[7] = 1566844251, d[7] = 4199065

Example 11 - 1 (continue)

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Passing arrays to functions

To pass an array to a function - the name of the array is passed

To pass a single element of an array to a function - simply pass the name of the array followed by the subscript of the particular element.

C passes arrays to functions by reference – the called functions can modify the element values in the caller’s original arrays.

The name of the array is actually the address of the first element of the array

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Passing arrays to functions (continue)

When the called function modifies array elements in its function body, it is modifying the actual elements of the array in their original memory location.

To receive an array argument, the function’s parameter list must specify that an array will be received. The size of that array is also needed.

An example:

int findmax(int this_array[ ], int size);

int findmax(int *this_array, int size)

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Example 11 - 2 /*A simple program uses functions for swapping and

printing data elements in a two-dimensional array. */#include <stdio.h>void swap(int *, int *); /* Function Prototypes */void print(void); /* Function Prototypes */static int data[2][2] = { {1, 2}, {3, 4}};void main(){ int x, y; puts("\nBefore swapping"); print(); swap(&data[0][0], &data[1][1]); swap(&data[0][1], &data[1][0]); puts("\nAfter swapping"); print();}

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void swap(int *a, int *b){ int temp; temp = *a; *a = *b; *b = temp;}void print(void){ int r, c; for(r = 0; r < 2; r++) for(c = 0; c < 2; c++) { printf("\ndata[%d][%d] = %d",r,c,data[r][c]); }}

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Output:

Before swapping After swappingdata[0][0] = 1 data[0][0] = 4data[0][1] = 2 data[0][1] = 3data[1][0] = 3 data[1][0] = 2data[1][1] = 4 data[1][1] = 1


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Example 11 - 3

/* Passing arrays and individual array elements to functions */

#include <stdio.h>#define SIZE 5

/* function prototypes */void modifyArray( int b[], int size ); void modifyElement( int e );

/* function main begins program execution */int main(){ int a[ SIZE ] = {0, 1, 2, 3, 4}; /* initialize a */ int i; /* counter */

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printf( "Effects of passing entire array by reference:\n\nThe " "values of the original array are:\n" );

/* output original array */ for ( i = 0; i < SIZE; i++ ) { printf( "%3d", a[ i ] ); } /* end for */ printf( "\n" );

/* pass array a to modifyArray by reference */ modifyArray( a, SIZE ); printf( "The values of the modified array are:\n" );

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/* output modified array */ for ( i = 0; i < SIZE; i++ ) { printf( "%3d", a[ i ] ); } /* end for */

/* output value of a[ 3 ] */ printf( "\n\n\nEffects of passing array element " "by value:\n\nThe value of a[3] is %d\n", a[ 3 ] ); modifyElement( a[ 3 ] ); /* pass array element a[ 3 ] by value */

/* output value of a[ 3 ] */ printf( "The value of a[ 3 ] is %d\n", a[ 3 ] ); return 0; /* indicates successful termination */} /* end main */

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/* in function modifyArray, "b" points to the original array "a" in memory */

void modifyArray( int b[], int size ){ int j; /* counter */ /* multiply each array element by 2 */ for ( j = 0; j < size; j++ ) { b[ j ] *= 2; // b[ j ] = b[j ] * 2; } /* end for */} /* end function modifyArray */

/* in function modifyElement, "e" is a local copy of array element a[ 3 ] passed from main */

void modifyElement( int e ){ /* multiply parameter by 2 */ printf( "Value in modifyElement is %d\n", e *= 2 );} /* end function modifyElement */

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Sorting Elements in Arrays

Sorting is the process of rearranging the elements of an array into numerical order (either ascending or descending).• Bubble sort, Selection sort, Quick sort, etc• Min, Max elements• Help data analysis

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After the sorting• min = a[ 0 ] – smallest element• Max = a[size -1] -- largest element• Middle element

Using bubble sort (sinking sort) – the smaller value upward to the top while the larger values sink to the bottom of the array

Bubble sort is performed by the two nested for loops and a swap function

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Bubble Sort• Before sorting

d_array = [76 45 1 82 44]• After sorting

d_array = [1 44 45 76 82] Steps (repeated until no swaps take place)

• If the first element of x is greater than the second element of x, swap their positions in the vector.

• If the second element of x is greater than the third element of x, swap their positions in the vector.

• · · · · · · · · ·• If the next-to-last element of x is greater than the

last element of x, swap their positions in the vector

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Bubble Sort – Example 11-4/* bubblesort.c */#include <math.h>#include <stdio.h>#define MAX 10int no[MAX];unsigned long int next = 1;/* rand(): return psedo-random integer from 0...32767 */int rand(void) { next = next * 1103515245 + 12345; return (unsigned int) (next/65536) % 32768; }/* srand: set seed for rand() */void srand(unsigned int seed) { next = seed; }

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Bubble Sort – Example 11-4 (cont.)

void sort(int data[], int size) { int upper, lower, temp; // Loop for counting the number of passes

for(upper = 0; upper < size -1; upper++) { // Loop for comparison and exchange

for(lower = upper + 1; lower < size; lower++) {

if(data[upper] > data[lower]) { temp = data[lower]; data[lower] = data[upper]; data[upper] = temp; }

} }

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void main() { int i, number, found; unsigned int j;

for(i = 0; i < MAX; ++i) { no[i] = j = rand(); printf("Random number(%d) =

%u\n", i,j); srand(i+2); }

/* bubble sort */ sort(no, MAX); /* display sorted array */ for(i = 0; i < MAX; ++i) { printf("no[%d] = %u\n", i, no[i]); } puts("Enter a number for searching"); scanf("%d", &number); }

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Running Results:

Random number(0) = 16838Random number(1) = 908Random number(2) = 17747Random number(3) = 1817Random number(4) = 18655Random number(5) = 2726Random number(6) = 19564Random number(7) = 3634Random number(8) = 20472Random number(9) = 4543no[0] = 908no[1] = 1817no[2] = 2726no[3] = 3634no[4] = 4543no[5] = 16838no[6] = 17747no[7] = 18655no[8] = 19564no[9] = 20472

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Searching Elements in Arrays

Determine whether an array contains a value that matches a certain key value.

The process of finding a particular element of an array is searching.

Type of searching:• Linear search – compares each element of the array

with the search key• Brainy search – eliminates from consideration one half

of the elements in a sorted array after each comparison. The worse case of searching is n times, where n is 2 to the power of n or 2n

Examples: • An array of 1023 elements will take less then 10

comparisons using brainy search. 1023 < 210

• An array of 65536 elements will take less then 16 comparisons using brainy search. 65535 < 216

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Binary Search – Example 11-5/* bubblesort.c */#include <math.h>#include <stdio.h>#define MAX 10int no[MAX];unsigned long int next = 1;/* rand(): return psedo-random

integer from 0...32767 */int rand(void) { next = next * 1103515245 + 12345; return (unsigned int) (next/65536)

% 32768; }/* srand: set seed for rand() */void srand(unsigned int seed) { next = seed; }

void sort(int data[], int size){ int upper, lower, temp; // Loop for counting the number of passes for(upper = 0; upper < size -1; upper++) { // Loop for comparison and exchange for(lower = upper + 1; lower < size; lower++) {

if(data[upper] > data[lower]) { temp = data[lower]; data[lower] = data[upper]; data[upper] = temp; }

} }

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Binary Search – Example 11-5 (cont.)

int binsearch(int x, int no[], int n){ int low, high, mid;

low = 0; high = n-1; mid = (low + high) /2; while(low <= high && x != no[mid]) {

if(x < no[mid]) high = mid -1; else low = mid + 1; mid = (low + high)/2;}

if (x == no[mid])return mid; /* found match */

elsereturn -1; /* no match */

}

void main(){ int i, number, found; unsigned int j;

for(i = 0; i < MAX; ++i) { no[i] = j = rand(); printf("Random

number(%d) = %u\n", i,j);

srand(i+2); } /* bubble sort */ sort(no, MAX);

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/* display sorted array */ for(i = 0; i < MAX; ++i) { printf("no[%d] = %u\n", i, no[i]); } puts("Enter a number for searching"); scanf("%d", &number);

/* binary search */ found = binsearch(number, no, MAX); if(found == -1) puts("Cant' find a match"); else printf("The number is in no[%d]\n", found);

}

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Running ResultRandom number(0) = 16838Random number(1) = 908Random number(2) = 17747Random number(3) = 1817Random number(4) = 18655Random number(5) = 2726Random number(6) = 19564Random number(7) = 3634Random number(8) = 20472Random number(9) = 4543no[0] = 908no[1] = 1817no[2] = 2726no[3] = 3634no[4] = 4543no[5] = 16838no[6] = 17747no[7] = 18655no[8] = 19564no[9] = 20472Enter a number for searching18655The number is in no[7]

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Multiple-subscripted arrays

A common use of multiple-subscripted arrays is to represent tables of values consisting of information arranged in rows and columns.

Table or arrays require two subscripts to identify a particular element.

Example: m by n array means an array with m rows and n columns

To pass one row of a double-subscripted array to a function that receives a single-subscripted array, simply pass the name of the array followed by the subscript of that row.

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Multiple-subscripted arrays (continue)

Example 11-6: Multiple subscripted arrays can have more

than two subscripts A multiple subscripted array can be initialized

when it is defined as the same way as the 1-D example:static int my_array[4][2][3] =

{ {{1, 2, 3}, { 4, 5, 6}}, {{7, 8, 9}, {10, 11, 12}}, {{13, 14, 15}, {16, 17, 18}}, {{19, 20, 21}, {22, 23, 24}} };

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/* Find the minimum grade of any student for the semester */int minimum( const int grades[ ][ EXAMS ], int pupils, int tests ){ int i; /* student counter */ int j; /* exam counter */ int lowGrade = 100; /* initialize to highest possible grade */ /* loop through rows of grades */ for ( i = 0; i < pupils; i++ ) { /* loop through columns of grades */ for ( j = 0; j < tests; j++ ) { if ( grades[ i ][ j ] < lowGrade ) { lowGrade = grades[ i ][ j ]; } /* end if */ } /* end inner for */ } /* end outer for */ return lowGrade; /* return minimum grade */ } /* end function minimum */

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/*Determine the average grade for a particular student */double average( const int setOfGrades[ ], int tests ){ int i; /* exam counter */ int total = 0; /* sum of test grades */

/* total all grades for one student */ for ( i = 0; i < tests; i++ ) { total += setOfGrades[ i ]; } /* end for */ return ( double ) total / tests; /* average */} /* end function average */

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Programming Applications

Example 11-7: Arithmetic Mean of N Numbers

#define N 5main(){ float x[N] = {1.0, 2.0, 3.0, 4.0, 5.0}; float mean = 0.0; int i;

for(i = 0; i < N; i++)mean += x[i];

mean /= N; printf(“mean = %f”, mean);

}

meann

xx x x x

nii

nn

11

1 2 3 ...

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Calculating the Sine using Series Approximation

Example 11-8: A Sine function repeats itself every 2 radians. Using the sine series for an approximation of the sin(x) function:

/* Program: sinesr.c - Approximation of the sin(x) function */

#define REG_TO_RAD 180.0/PI/* sinesr.c */#include <math.h>#include <stdio.h>#define PI 3.14159#define DEG_TO_RAD (180.0/PI) /* 57.29577951308232 */

sin! ! ! ! !

...x xx x x x x

3 5 7 9 11

3 5 7 9 11

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Calculating the Sine using Series (continue)

#define x2(x) (x * x) /* Macro for x ^2 */#define x3(x) (x * x * x) /* Macro for x^3 */#define x5(x) (x*x*x*x*x) /* Macro for x^5 */#define x7(x) (x*x*x*x*x*x*x) /* Macro for x^7 */#define x9(x) (x*x*x*x*x*x*x*x*x) #define FAC3 (1*2*3) /* Factorial 3 */#define FAC5 (1*2*3*4*5) /* Factorial 5 */#define FAC7 (1*2*3*4*5*6*7) /* Factorial 7 */#define FAC9 (1*2*3*4*5*6*7*8*9)void main(void)

{

double sinSER, sinLIB, error, x, n;

printf("Deg Radians Sine Series Sin(x) Error\n");

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printf("_________________________________________\n");for(n = 0.0; n <= 90.0; n+=5.0){

x = n/DEG_TO_RAD; /*convert degree to radians*/ sinLIB = sin(x); sinSER = x - (x3(x)/FAC3)+ (x5(x)/FAC5)- (x7(x)/FAC7)+ (x9(x)/FAC9);

error = sinSER - sinLIB; printf("%5.2lf %9.8lf %9.8lf %9.8lf %+.6e\n",

n, x, sinLIB, sinSER, error); } printf("__________________________\n");

}

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Output:Deg Radians Sine Series Sin(x) Error__________________________________________________ 0.00 0.00000000 0.00000000 0.00000000 +0.000000e+000 5.00 0.08726639 0.08715567 0.08715567 +0.000000e+00010.00 0.17453278 0.17364803 0.17364803 +1.110223e-01615.00 0.26179917 0.25881883 0.25881883 +9.936496e-01520.00 0.34906556 0.34201987 0.34201987 +2.347011e-01325.00 0.43633194 0.42261793 0.42261793 +2.730927e-01230.00 0.52359833 0.49999962 0.49999962 +2.027972e-01135.00 0.61086472 0.57357601 0.57357601 +1.104591e-01040.00 0.69813111 0.64278716 0.64278716 +4.795073e-01045.00 0.78539750 0.70710631 0.70710631 +1.750303e-009

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50.00 0.87266389 0.76604397 0.76604397 +5.572419e-00955.00 0.95993028 0.81915158 0.81915160 +1.588251e-00860.00 1.04719667 0.86602496 0.86602500 +4.131496e-00865.00 1.13446306 0.90630738 0.90630748 +9.953193e-00870.00 1.22172944 0.93969227 0.93969249 +2.246074e-00775.00 1.30899583 0.96592554 0.96592602 +4.790796e-00780.00 1.39626222 0.98480755 0.98480852 +9.729044e-00785.00 1.48352861 0.99619459 0.99619648 +1.892315e-00690.00 1.57079500 1.00000000 1.00000354 +3.542551e-006___________________________________________________

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Summary

Determine Size of Arrays Passing Arrays to Functions Sorting/Searching Arrays Multiple Subscripted Arrays Programming Applications Next – C Pointers

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Answers

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