�ݺ�ߣ

contents
 Loop statement:
– While statement
– For statement
– do-while statement

 Statement for loop:
– break, continue,

 Examples

2

While Statement
 while statement type 1
– Repeat statement block( {…} ) while expression is true

F
expression
expression while( expression )
T
A
{
A C A;
B;
B
B }

C C;

3

While Statement
 while statement type 2
– In C world, 0(zero) means FALSE and other values means TRUE
– So while(1) indefinitely repeats its statement block
– You should place if…break in statement block for program to
escape from loops
while( 1 )
{
A A;
if( !expression ) break ;
F B;
expression }
T
B C C;

4

While Statement
 Note

while (1) i++; /* infinite loop */
while(5/3) i++;
while(-1) i++;

while(0) i++; /*naver runs*/

5

While Statement
 Transform type1 to type2

A A;
A
F while( expression )
expression
F {
expression T B;
T B C A;
B C }
A C;

6

Do-while Statement
 Special form of while statement 1
– while statement checks expression before executing
statements in the loop.
– On the contrary, do-while statement check expression
after executing statements in the loop.

do
A {
A;
B;
B
} while( expression ) ;
F
expression C;
T
C

7

For Statement
 Special form of while statement 2

for( A ; expression ; D)
A
{
F B;
expression C;
T }
B E E;

C
A: initial statement of loop statements
D D: end statement of loop statements

8

For Statement
 for statement vs. while statement

for ( expr1; expr2; expr3 ) expr1;
while (expr2)
{
{
statement ;
statement ;
... ...
} expr3;
next statement ; }
next statement ;

9

For Statement
 Example: Add even numbers from 1 to 100
Start int i, sum ;
sum = 0 ;
Var i, sum i=2;
while( i <= 100 ) {
sum = sum + i ;
sum <- 0 i =+ 2 ;
}
i <- 2 printf( “%dn”, sum ) ;

F int i, sum ;
i  100 sum = 0 ;
T
sum for( i = 2 ; i <= 100 ; i =+ 2) {
sum <- sum + i sum = sum + i ;
}
i <- i + 2 Stop printf( “%dn”, sum ) ;

10

For Statement
 Example: Read 10 numbers and sum up those

int i, n ; int i, n ;
sum= 0 ; sum = 0 ;
i= 0 ; for( i = 0 ; i < 10 ; i++ )
while ( i < 10) { {
scanf( “%d”, &n ) ; scanf( “%d”, &n ) ;
sum += n ; sum += n ;
i++ ; }
} printf( “%dn”, sum ) ;
printf( “%dn”, sum ) ;

11

For Statement
 Loop from 0 to n-1
for ( i = 0; i < n; i++ ) A;

 Loop from 1 to n
for ( i = 1; i <= n; i++ ) A;

 Loop from n-1 to 0
for ( i = n -1; i >= 0; i-- ) A;

 Loop from n to 1
for ( i = n; i > 0; i-- ) A;

12

Break Statement
 break
– Exit from the current loop or switch statement to terminate
while(A) {
B;
while(C) {
D;
if( E ) break;
F;
}
G;
if( H ) break ;
I ;
}
J;

13

Continue Statement
 continue
– Skip the rest of the statements in the loop
while(A) {
B;
while(C) {
D;
if( E ) continue;
F;
}
G;
if( H ) continue ;
I;
}
J;

14

Continue Statement
 continue
while(A) { while(A) {
B; B;
while(C) { while(C) {
D; D;
if( E ) continue; if( !E ) {
F; F;
G; G;
} }
H; }
if( I ) continue ; H;
J; if( !I ) {
K; J;
} K;
L; }
}
L;
15

Example
 Print all combinations of three numbers of
which sum equals to seven
007 #include <stdio.h>
016
025 void main(void)
034 {
… int i, j, k ;
502
511 for ( i = 0; i <= 7; ++i ) {
… for( j = 0; j <= 7; ++j ) {
610 for ( k = 0; k <= 7; ++k ) {
700 if ( i + j + k == 7 )
printf( "%d %d %dn", i, j, k );
}
}
}
return ;
}

16

Example 1
 Add all integers between 1 and 100
Start #include <stdio.h>

main() {
Var i, sum int i, sum ;

i =0;
i <- 1 sum = 0 ;

while( i <= 100 )
{
sum <- 0 sum = sum + i ;
i=i+1;
F }
i  100
printf( “%d”, sum ) ;
T
sum return ;
sum <- sum + i }

i <- i + 1 Stop

17

Example 1-1
 Add all integers between 1 and 100

main() {

i =0;
i <- 1 sum = 0 ;

while( i <= 100 )
{
sum <- 0 sum = sum + i ;
i=i+1;
}
i  100

sum <- sum + i sum return ;
}

i <- i + 1
Stop

18

Example 2
 Add all even integers between 1 and 100

main() {

i =0;
i <- 1, sum <- 0 sum = 0 ;

while( i <= 100 )
{
i  100 if( i % 2 == 0 )
{
i is even ? sum sum = sum + i ;
F }
T i=i+1;
}
sum <- sum + i
Stop

i <- i + 1 return ;
}

19

Example 3
 Find the largest n such that 1+2+…+n<1000
#include <stdio.h>
Start
main() {

Var n, sum int n, sum ;

n =1;
n <- 1, sum <- 0 sum = 0 ;

while( 1)
{
sum <- sum + n sum = sum + n ;
if( sum < 1000) break ;
n=n+1;
F n-1 }
sum < 1000
T printf( “%d”, n-2 ) ;

n <- n + 1 Stop return ;
}

20

Example 3-1
 Find the largest n such that 1+2+…+n<1000
Start
#include <stdio.h>

main() {
Var n, sum
int n, sum ;

n <- 1, sum <- 0 n =1;
sum = 0 ;

sum = sum + n ;
sum <- sum + n
while( sum < 1000 )
{
sum < 1000 n-1
n=n+1;
sum = sum + n ;
}
n <- n + 1
Stop
printf( “%d”, n-2 ) ;
sum <- sum + n
return ;
}

21

Example 4
 (1+1+…+1)+ … + (10+10+…+10)
Start
#include <stdio.h> #include <stdio.h>
Var a, b, sum
main() main()
{ {
a = 1, sum = 0 int a, b, sum; int a, b, sum;

sum = 0 ; sum = 0 ;
a  10 a=1; for( a=1; a<=10 ; a++ )
sum while( a <= 10 ) {
{ for( b=1; b<=10 ; b++ )
b <- 1 b=1; {
while( b <= 10 ) sum = sum + a ;
Stop { }
b  10 sum = sum + a ; }
b=b+1;
sum = sum+ a } return ;
a=a+1; }
}
b=b+1
return ;
}
a=a+1

22

Example 5
 (2*1+2*2+…+2*9)+ … + (9*1+9*2+…+9*9)
Start
#include <stdio.h> #include <stdio.h>
Var a, b, sum
main() main()
{ {
a = 2, sum = 0 int a, b, sum; int a, b, sum;

sum = 0 ; sum = 0 ;
a9 a=2; for( a=2; a<=9 ; a++ )
sum while( a <= 9 ) {
{ for( b=1; b<=9 ; b++ )
b <- 1 b=1; {
while( b <= 9 ) sum = sum + a*b ;
Stop { }
b9 sum = sum + a*b ; }
b=b+1;
sum = sum+ a * b } return ;
a=a+1; }
}
b=b+1
return ;
}
a=a+1

23

Example 6
 1+(1+2)+(1+2+3)+......+(1+....+10)
Start #include <stdio.h> #include <stdio.h>

main() main()
Var n, a, { {
sum int n, a, sum ; int a, b, sum;

n=1; sum = 0 ;
n <- 1, sum <- 0 a=1; for( n=1; n<=10 ; n++ )
sum = 0 ; {
for( a=1; a<=n ; a++ )
n  10 while( n <= 10 ) {
{ sum = sum + a ;
a=1; }
a <- 1 sum while( a <= n ) }
{
an sum = sum + a ; return ;
a=a+1; }
Stop }
sum <- sum + a n=n+1;
}
a <- a + 1

return ;
n <- n + 1 }
24

�ݺ�ߣ

4. loop

More Related Content

4. loop