7. arrays

Contents

 One-Dimensional Arrays

 Initialization

 Subscripting

2

One-Dimensional Arrays
 Array
– A set of variables sharing the name

int num[5] ;

– 5 variables will be consecutively creased with the name of “num”

num

address 1000 1004 1008 1012 1016

3

 Accessing Members of Array
– Using index
– The index of the first member is 0

int num[5] ; num[1] num[2] num[3] num[4]
num[0]

num[0] = 10 ; num 10 13 14 17 20

num[1] = 13 ;
num[2] = 14 ; 1000 1004 1008 1012 1016
num[3] = 17 ;
address
num[4] = 20 ;

4

 Accessing Members of Array

char ch[7] ;
ch[0] ch[1] ch[2] ch[3] ch[4] ch[5] ch[7]
ch[0] = ‘a’ ; ch a b c d e f g
ch[1] = ‘b’ ;
ch[2] = ‘c’ ; 1000 1001 1004 1005 1006
1002 1003
ch[3] = ‘d’ ; address
ch[4] = ‘e’ ;
ch[5] = ‘f’ ;
ch[6] = ‘g’ ;

5

 Some Frequent Errors

element-type array_name[size];

[Ex] int grade[50]; size of Array

data type variable Name

– “size of array” should be a positive constant
– “index” are from 0 to N-1
• In the example, grade[0], grade[1],~ , grade[49]

6

 Example
double student[10] ;
int aaa[10+5] ;
For declaration,
you cannot use variables
int k = 5 ;
char ch[k] ;

int num[10] ;
int k = 0 ;
For member access,
you can use variables and
num[1] = 1 ;
any expressions.
num[2+3] = 9 ;
num[k] = 0 ;
num[k++] = 2 ;
num[k+3] = 4 ;

7

 Example
a[0] = 0, a[1] = 1, a[2] = 2, ..., a[9] = 9

void main() { void main() {
int a[10], k ; int a[10], k ;

for( k = 0 ; k < 10 ; k++ ) k = 0 ;
a[k] = k ; while(k < 10)
} {
a[k] = k ;
k++ ;
}
}

8

 Initialization each value will be assigned
to each member
int a[5];
int a[5] = {1, 5, 3, 7, 6} ;
a[0] = 1 ;
a[1] = 5 ;
a[2] = 3 ;
a[3] = 7 ;
a[4] = 6 ; int a[5];

if the number is less, a[0] = 1 ;
other members will be 0
a[1] = 4 ;
a[2] = 0 ;
int a[5] = {1, 4} ; a[3] = 0 ;
a[4] = 0 ;

9

Reverse Printing
 Example
#include <stdio.h> #include <stdio.h>

void main() { void main() {
int a[10], k ; int a[10], k;

for( k = 0 ; k < 10 ; k++ ) k=0 ;
scanf( “%d”, &a[k] ) ; while(k < 10)
scanf( “%d”, &a[k++] ) ;
for( k = 9 ; k >= 0 ; k-- )
printf( “%d ”, a[k] ) ; k=9;
while(k >= 0)
printf( “n” ) ; printf( “%d ”, a[k--] ) ;
}
printf( “n” ) ;
}

10

Inner Product
 Read 2 vectors (3 dimensional) and evaluate
the inner product
#include <stdio.h>
1 2 3
4 -5 6
void main()
12
{
int a[3], b[3], k, p ;

for( k=0;k<3;k++) scanf(“%d”, &a[k] ) ;
for( k=0;k<3;k++) scanf(“%d”, &b[k] ) ;

p = 0 ;
for( k=0;k<3;k++) p += a[k]*b[k] ;
}

11

Rotation
 Read 5 numbers and rotate it to the right
[0] [1] [2] [3] [4] #include <stdio.h>
num: 10 9 2 4 5
void main()
{
int num[5], k, tmp ;
tmp = num[0] ;
num[1] = num[0] ; for( k = 0 ; k < 5 ; k++ )
num[0] = num[1] ;
num[2] = num[1] ; scanf( “%d”, &num[k] ) ;
num[1] = num[2] ;
num[3] = num[2] ;
num[2] = num[3] ;
num[4] = num[3] ; tmp = num[0] ;
num[3] = num[4] ;
num[0] = num[4] ; for( k = 0 ; k < 4 ; k++ )
num[4] = tmp ;
num[k] = num[k+1] ;
num[4] = tmp ;
}

12

Counting Numbers
 Example Program
– Counting numbers Start
true

1 0 9 4 5 3 2 7 9 6 4 1 -1 num[10], k, n
n
F
0: 1 k = 0 ; k < 10 ; k++
n<0
1: 2
num[k] = 0 T
2: 1
num[n]++ break
3: 1
4: 2
5: 1
k = 0 ; k < 10 ; k++
6: 1
7: 1 k “:” num[k]
8: 0
9: 2
Stop

13

Counting Numbers
 Example Program
#include <stdio.h>

void main(void) {
int num[10], n, k ;

for( k = 0 ; k < 10 ; k++ ) num[k] = 0 ;

while ( 1 ) {
scanf( “%d”, &n ) ;
if( n < 0 ) break ;
num[n]++ ;
}

for( k = 0 ; k < 10 ; k++ )
printf( “%d:%dn”, k, num[k] ) ;
}
14

Find Maximum
 Read 10 numbers and print the maximum
10 9 2 4 5 -9 27 -4 -2 14

Maximum: 27

10 9 2 4 5 -9 27 -4 -2 14

15

Find Maximum
 순서도로 그리면…

Start
pos <- 0
num[10], i,
pos i = 1 ; i < 10 ; i++

i = 0 ; i < 10 ; i++ num[pos] < num[i]
F
x T
pos <- i

num[pos]

Stop

16

Find Maximum
 Example Program
#include <stdio.h>

void main(void) {
int num[10], i, pos;

for( i = 0 ; i < 10 ; i++ ) scanf(“%d”, &num[i] ) ;

pos = 0 ;
for( i = 1 ; i < 10 ; i++ ) {
if( num[pos]< num[i] ) pos = i ;
}

printf( “Maximum:%dn”, num[pos] );
}

17

Find Second Largest
 Read 10 numbers and print the second largest

10 9 2 4 5 -9 27 -4 -2 14

Second Largest: 10

10 9 2 4 5 -9 27 -4 -2 14

27 9 2 4 5 -9 10 -4 -2 14

18

Find Second Largest
 Example Program
#include <stdio.h> pos = 1 ;
for( i = 2 ; i < 10 ; i++ )
void main(void) { if( num[pos] < num[i] ) pos = i ;
int num[10], i, pos, tmp ;
printf( “Second Largest:%dn”,
for( i = 0 ; i < 10 ; i++ ) num[pos] ) ;
scanf(“%d”, &num[i] ) ; }

pos = 0 ;
for( i = 1 ; i < 10 ; i++ )
if( num[pos] < num[i] ) pos = i ;

tmp = num[0] ;
num[0] = num[pos] ;
num[pos] = tmp ;
19

Sort Numbers
 Read 10 numbers and print in the descending
order
10 9 2 4 5 -9 27 -4 -2 14
10 9 2 4 5 -9 27 -4 -2 14

27 14 10 9 5 4 2 -2 -4 -9 27 9 2 4 5 -9 10 -4 -2 14

27 14 2 4 5 -9 10 -4 -2 9

27 14 10 4 5 -9 2 -4 -2 9

27 14 10 9 5 4 2 -2 -4 -9

20

Sort Numbers
 Example Program pos = 1 ;
for( i = 2 ; i < 10 ; i++ )
#include <stdio.h> if( num[pos] < num[i] ) pos = i ;

void main(void) { tmp = num[1] ;
int num[10], i, pos, tmp ; num[1] = num[pos] ;
num[pos] = tmp ;
for( i = 0 ; i < 10 ; i++ )
scanf(“%d”, &num[i] ) ; pos = 2 ;
for( i = 3 ; i < 10 ; i++ )
pos = 0 ; if( num[pos] < num[i] ) pos = i ;
for( i = 1 ; i < 10 ; i++ )
if( num[pos] < num[i] ) pos = i ; tmp = num[2] ;
num[2] = num[pos] ;
tmp = num[0] ; num[pos] = tmp ;
num[0] = num[pos] ;
num[pos] = tmp ; ...
} 21

Sort Numbers
 Example Program
#include <stdio.h>
for( j = 0 ; j < 9 ; j++ )
void main(void) { {
int num[10], i, j, pos, tmp ; pos = j ;

for( i = 0 ; i < 10 ; i++ ) for( i = j+1 ; i < 10 ; i++ )
scanf(“%d”, &num[i] ) ; if( num[pos] < num[i] ) pos = i ;

... tmp = num[j] ;
num[j] = num[pos] ;
for( j = 0 ; j < 9 ; j++ ) num[pos] = tmp ;
printf( “%d “, num[j] ) ; }
}

22

7. arrays

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7. arrays