Lesson 15 - Learning Goals
15.1 Learn the C constructs for looping
15.2 Learn how to use the C do loops
15.3 Learn how to use the C while loops
15.4 Learn how to use the C for loop
While loop
- test at beginning
Is logical expression true ?
If YES, go through the loop statements.
If NO, do not execute the while
loop.
EXAMPLE :
/* How many digits ? */
ndigit = 1;
number = 10000 ;
while ( number >= 10 ) {
number = number / 10 ;
ndigit = ndigit + 1 ;
}
Do loop
- test at end
Do the loop once ( execute loop statements ).
Then, is logical expression true
?
If YES, go through the loop statements
again.
If NO, exit the loop.
/* How many digits ? */
ndigit = 0;
number = 10000 ;
do
{
number = number / 10 ;
ndigit = ndigit + 1 ;
} while ( number != 0 ) ;
SCANF
#include <stdio.h>
main( )
{
int d1, d2, d3, d4, d5, d6, d7 ;
while ( scanf(''%1d%1d%1d%1d%1d%1d%1d'',
&d1, &d2, &d3, &d4, &d5, &d6, &d7) = = 7 )
{
printf ('' Reverse : %1d%1d%1d%1d%1d%1d%1d \n'',
d7, d6, d5, d4, d3, d2, d1 ) ;
}
}
EXAMPLE :
***************************************************
Input
Output
1234567 Reverse : 7654321
7 6 5 4 3 2 1 Reverse : 1234567
0987654 2345678 Reverse : 4567890
Reverse : 8765432
1234567890 Reverse : 7654321
1234 Reverse : 4321098
SCANF
#include <stdio.h>
main( )
{
char cmd [ 15 ] ;
int i ;
i = scanf ('' %s '', cmd ) ; /* No & before cmd because cmd
is an array */
if ( i = = -1 ) printf ('' Blank input \n '') ;
else printf (''The input is %s \n '', cmd) ;
}
Input : 23456
Output : Blank input
scanf returns a function value equal to the number of good arguments.
It returns 0 if there is no input,
and -1 if EOF (end of file)
FOR loop
- general loop form
for ( Initialize ; logical expression
; update variable )
Is logical expression true ?
If YES, go through the loop statements.
Then, Update the initial condition
Is logical expression true ?
If YES, go through the loop statements.
Then, Update the initial condition
Is logical expression true ?
.
.
.
If NO, exit the loop.
EXAMPLE :
/* Execute the same statement 10 times */
for( i=0 ; i < 10 ; i++ )
{
j = j + 1 ;
}
FOR loop in C
for ( init, init, . . . , init ;
expression ;
update, update, . . . , update )
{
statements ;
}
Example :
for ( ndigit = 1; number >= 10 ; ndigit += 1 )
{
number = number/10 ;
}
Differences from FORTRAN
:
Go back to lecture menu
Go back to main page