Introduction to Computing
Lecture 07:
Repetition and Loop Statements
(Part II)
Assist.Prof.Dr. Nükhet ÖZBEK
Ege University
Department of Electrical & Electronics Engineering
nukhet.ozbek@ege.edu.tr
Topics
 break statement
 continue statement
 Infinite loops
 Nested loops
 while and for
 Macros
 Example
 Factorization
The break statement
• Implements the "exit loop" primitive
• Causes flow of control to leave a loop
block (while or for) immediately
The continue statement
• Causes flow of control to start immediately
the next iteration of a loop block (while
or for)
Infinite Loops
while ( 1 )
{
...etc...etc...etc...
}
for ( ; 1 ; )
{
...etc...etc...etc...
}
for ( ; ; )
{
...etc...etc...etc...
}
Use an:
if ( condition )
{
break;
}
statement to break the loop
Example: addpos.c
Read in numbers, and add
only the positive ones. Quit
when input is 0
set sum to 0
loop
{
input number
if (number is negative)
{
begin next iteration
}
else if ( number is zero)
{
exit loop
}
add number to sum
}
output sum
Example: addpos.c (cont)
Read in numbers, and add
only the positive ones. Quit
when input is 0
set sum to 0
loop
{
input number
if (number is negative)
{
begin next iteration
}
else if ( number is zero)
{
exit loop
}
add number to sum
}
include <stdio.h>
/****************************
** Read in numbers, and add
** only the positive ones.
** Quit when input is 0
*****************************/
int main()
{
float num, sum = 0.0;
printf("sum = %f\n", sum);
return 0;
output sum
}
Example: addpos.c (cont)
Read in numbers, and add
only the positive ones. Quit
when input is 0
set sum to 0
loop
{
input number
if (number is negative)
{
begin next iteration
}
else if ( number is zero)
{
exit loop
}
add number to sum
}
include <stdio.h>
/****************************
** Read in numbers, and add
** only the positive ones.
** Quit when input is 0
*****************************/
int main()
{
float num, sum = 0.0;
while (1)
{
scanf("%f", &num);
sum += num;
}
printf("sum = %f\n", sum);
return 0;
output sum
}
Example: addpos.c (cont)
Read in numbers, and add
only the positive ones. Quit
when input is 0
set sum to 0
loop
{
input number
if (number is negative)
{
begin next iteration
}
else if ( number is zero)
{
exit loop
}
include <stdio.h>
/****************************
** Read in numbers, and add
** only the positive ones.
** Quit when input is 0
*****************************/
int main()
{
float num, sum = 0.0;
while (1)
{
scanf("%f", &num);
if (num < 0)
continue;
else if (num == 0)
break;
sum += num;
add number to sum
}
}
output sum
printf("sum = %f\n", sum);
return 0;
}
Example: addpos.c (cont)
include <stdio.h>
Read in numbers, and add
only the positive ones. Quit
when input is 0
/****************************
** Read in numbers, and add
** only the positive ones.
** Quit when input is 0
*****************************/
set sum to 0
int main()
{
float num, sum = 0.0;
loop
{
input number
if (number is negative)
{
begin next iteration
}
else if ( number is zero)
{
exit loop
}
while (1))
{
scanf("%f", &num);
if (num < 0)
continue;
else if (num == 0)
break;
add number to sum
sum += num;
}
}
output sum
printf("sum = %f\n", sum);
return 0;
}
Example: addpos.c (cont)
Read in numbers, and add
only the positive ones. Quit
when input is 0
set sum to 0
loop
{
input number
if (number is negative)
{
begin next iteration
}
else if ( number is zero)
{
exit loop
}
include <stdio.h>
/****************************
** Read in numbers, and add
** only the positive ones.
** Quit when input is 0
*****************************/
int main()
{
float num, sum = 0.0;
while (1)
{
scanf("%f", &num);
if (num < 0)
continue;
else if (num == 0)
break;
sum += num;
add number to sum
}
}
output sum
printf("sum = %f\n", sum);
return 0;
}
for and continue
• In the case of a for statement, control
passes to the “update” expression.
Example:
for (a = 0; a < 100; a++)
{
if (a%4)
continue;
printf(“%d\n”,a);
}
Nested Loops - Example: rect.c
Print an m by n rectangle of
asterisks
input width and height
for each row
{
for each column in the current row
{
print an asterisk
}
start next row
}
Example: rect.c (cont)
#include <stdio.h>
/*
Print an m by n rectangle of
asterisks
Print an m-by-n rectangle of
asterisks */
int main()
{
int i, j, m, n;
printf("\nEnter width: ");
scanf("%d", &m);
printf("\nEnter height: ");
scanf("%d", &n);
input width and height
for each row
{
for each column in the current row
{
print an asterisk
}
start next row
}
return 0;
}
Example: rect.c (cont)
#include <stdio.h>
/*
Print an m by n rectangle of
asterisks
Print an m-by-n rectangle of
asterisks */
int main()
{
int i, j, m, n;
printf("\nEnter width: ");
scanf("%d", &m);
printf("\nEnter height: ");
scanf("%d", &n);
input width and height
for (i=0; i < n; i++)
{
for each row
{
for each column in the current row
{
print an asterisk
}
start next row
}
}
return 0;
}
Example: rect.c (cont)
#include <stdio.h>
/*
Print an m by n rectangle of
asterisks
Print an m-by-n rectangle of
asterisks */
int main()
{
int i, j, m, n;
printf("\nEnter width: ");
scanf("%d", &m);
printf("\nEnter height: ");
scanf("%d", &n);
input width and height
for (i=0; i < n; i++)
{
for (j=0; j < m; j++)
{
for each row
{
for each column in the current row
{
print an asterisk
}
start next row
}
}
}
return 0;
}
Example: rect.c (cont)
#include <stdio.h>
/*
Print an m by n rectangle of
asterisks
Print an m-by-n rectangle of
asterisks */
int main()
{
int i, j, m, n;
input width and height
printf("\nEnter width: ");
scanf("%d", &m);
printf("\nEnter height: ");
scanf("%d", &n);
for (i=0; i < n; i++)
{
for (j=0; j < m; j++)
{
printf("*");
}
for each row
{
for each column in the current row
{
print an asterisk
}
start next row
}
}
return 0;
}
Example: rect.c (cont)
#include <stdio.h>
/*
Print an m by n rectangle of
asterisks
Print an m-by-n rectangle of
asterisks */
int main()
{
int i, j, m, n;
input width and height
printf("\nEnter width: ");
scanf("%d", &m);
printf("\nEnter height: ");
scanf("%d", &n);
for each row
{
for each column in the current row
{
print an asterisk
}
start next row
}
for (i=0; i < n; i++)
{
for (j=0; j < m; j++)
{
printf("*");
}
printf("\n");
}
return 0;
}
Example: rect.c (cont)
#include <stdio.h>
/*
Print an m by n rectangle of
asterisks
Print an m-by-n rectangle of
asterisks */
int main()
{
int i, j, m, n;
printf("\nEnter width: ");
scanf("%d", &m);
printf("\nEnter height: ");
scanf("%d", &n);
input width and height
for (i=0; i < n; i++)
{
for (j=0; j < m; j++)
{
printf("*");
}
printf("\n");
}
for each row
{
for each column in the current row
{
print an asterisk
}
start next row
}
return 0;
}
Example: rect.c (cont)
#include <stdio.h>
/*
Print an m by n rectangle of
asterisks
Print an m-by-n rectangle of
asterisks */
int main()
{
int i, j, m, n;
algorithm
printf("\nEnter width: ");
scanf("%d", &m);
printf("\nEnter height: ");
scanf("%d", &n);
program
input width and height
for (i=0; i < n; i++)
{
for (j=0; j < m; j++)
{
printf("*");
}
printf("\n");
}
for each row
{
for each column in the current row
{
print an asterisk
}
start next row
}
return 0;
}
Variation: rect2.c
#include <stdio.h>
/*
Print an m by n rectangle of
asterisks
input width and height
for each row
{
for each column in the current row
{
print an asterisk
}
start next row
}
Print an m-by-n rectangle of
asterisks */
int main()
{
int i, j, m, n;
printf("\nEnter width: ");
scanf("%d", &m);
printf("\nEnter height: ");
scanf("%d", &n);
i = 0;
while (i < n)
{
for (j=0; j < m; j++)
{
printf("*");
}
printf("\n");
i++;
}
return 0;
}
Variation: rect3.c
Print an m by n rectangle of
asterisks
#include <stdio.h>
/* Print an m-by-n rectangle of
asterisks */
int main()
{
int i, j, m, n;
printf("\nEnter width: ");
scanf("%d", &m);
printf("\nEnter height: ");
scanf("%d", &n);
input width and height
for (i=0; i < n; i++)
{
j = 0;
while (1)
{
printf("*");
j++;
if (j == m)
break;
}
printf("\n");
}
return 0;
for each row
{
for each column in the current row
{
print an asterisk
}
start next row
}
}
Variation: rect3.c (cont)
#include <stdio.h>
/* Print an m-by-n rectangle of
asterisks */
int main()
{
int i, j, m, n;
printf("\nEnter width: ");
scanf("%d", &m);
printf("\nEnter height: ");
scanf("%d", &n);
for (i=0; i < n; i++)
{
j = 0;
while (1)
{
printf("*");
j++;
if (j == m)
break;
}
printf("\n");
}
return 0;
The innermost
enclosing loop
for this break is
the while-loop
}
while and for
• A for loop can always be rewritten as
an equivalent while loop, and vice-versa
• The continue statement in a for loop
passes control to the “update” expression
ASCII (American Standard Code for
Information Interchange)
• Is a character encoding based on the
English alphabet.
• ASCII codes represent text in computers,
communications equipment, and other
devices that work with text
• There are 128 characters (0-127)
• First 32 (0-31) are control characters and
are not printable
Example: asciiCheck.c
while (1)
{
printf("Enter bounds (low high): ");
scanf("%d %d", &low, &high);
if ((low >= 0) && (high <= 127) && (low < high))
{
break;
}
else
{
printf("Bad bounds. Try again.\n");
}
}
Example: asciiCheck.c
while (1)
{
printf("Enter bounds (low high): ");
scanf("%d %d", &low, &high);
if ((low >= 0) && (high <= 127) && (low < high))
{
break;
}
else
{
printf("Bad bounds. Try again.\n");
}
}
Example: asciiPrint
Print out a section of the ASCII table
for each character from the lower bound to higher bound
{
print its ascii value and ascii character
}
for ( ch = low; ch <= high; ch++ )
{
printf("%d: %c\n", ch, ch);
}
asciiPrint1.c
ch = low;
while ( ch <= high )
{
printf("%d: %c\n", ch, ch);
ch++;
}
asciiPrint2.c
Example: asciiPrint (cont)
for ( ch = low; ch <= high; ch++ )
{
printf("%d: %c\n", ch, ch);
asciiPrint1.c
}
ch = low;
while (1)
{
printf("%d: %c\n", ch, ch);
if (ch < high)
{
ch++;
continue;
}
else
{
break;
}
asciiPrint3.c
}
Example: asciiPrint (cont)
for ( ch = low; ch <= high; ch++ )
{
printf("%d: %c\n", ch, ch);
asciiPrint1.c
}
ch = low;
for (;;)
{
printf("%d: %c\n", ch, ch);
ch++;
if (ch > high)
{
break;
}
}
asciiPrint4.c
Example: ascii1.c
while (1)
{
printf("Enter bounds (low high): ");
scanf("%d %d", &low, &high);
if ((low >= MIN) && (high <= MAX)
&& (low < high))
{
break;
}
else
{
printf("Bad bounds. Try again.\n");
}
#include <stdio.h>
/* Print a section of
the ASCII table */
#define
#define
MIN
MAX
}
0
127
int main()
{
int low, high;
char ch;
for (ch=low; ch <= high; ch++)
{
printf("%d: %c\n", ch, ch);
}
return 0;
}
Example: ascii1.c
(cont)
while (1)
{
printf("Enter bounds (low high): ");
scanf("%d %d", &low, &high);
if ((low >= MIN) && (high <= MAX)
&& (low < high))
{
break;
}
else
{
printf("Bad bounds. Try again.\n");
}
#include <stdio.h>
/* Print a section of
the ASCII table */
#define
#define
MIN
MAX
}
0
127
int main()
{
int low, high;
char ch;
for (ch=low; ch <= high; ch++)
{
printf("%d: %c\n", ch, ch);
}
return 0;
}
Example: ascii1.c
(cont)
while (1)
{
printf("Enter bounds (low high): ");
scanf("%d %d", &low, &high);
if ((low >= MIN) && (high <= MAX)
&& (low < high))
{
break;
}
else
{
printf("Bad bounds. Try again.\n");
}
#include <stdio.h>
/* Print a section of
the ASCII table */
#define
#define
MIN
MAX
0
127
int main()
{
int low, high;
char ch;
}
for (ch=low; ch <= high; ch++)
{
printf("%d: %c\n", ch, ch);
}
Macro definition:
#define identifier tokens
return 0;
} subsequent instances of identifier
All
are replaced with its token
Output of Ascii1.c
Enter bounds (low high): 32 126
32:
33:!
34:"
35:#
42:*
43:+
44:,
45:52:4
53:5
54:6
55:7
62:>
63:?
64:@
65:A
72:H
73:I
74:J
75:K
82:R
83:S
84:T
85:U
92:\
93:]
94:^
95:_
102:f
103:g
104:h
105:i
112:p
113:q
114:r
115:s
122:z
123:{
124:|
125:}
36:$
46:.
56:8
66:B
76:L
86:V
96:`
106:j
116:t
126:~
37:%
47:/
57:9
67:C
77:M
87:W
97:a
107:k
117:u
38:&
48:0
58::
68:D
78:N
88:X
98:b
108:l
118:v
39:'
49:1
59:;
69:E
79:O
89:Y
99:c
109:m
119:w
40:(
50:2
60:<
70:F
80:P
90:Z
100:d
110:n
120:x
41:)
51:3
61:=
71:G
81:Q
91:[
101:e
111:o
121:y
Example : Factorization
• Write a program which prints out the
prime factorization of a number (treat 2 as
the first prime)
• For example,
on input 6, desired output is: 2 3
" " 24,
"
"
: 2223
" " 14,
"
"
: 27
" " 23,
"
"
: 23 (23 is
prime)
Algorithm
input n
set factor to 2
Algorithm
(cont)
input n
set factor to 2
while(some factor yet to try)
{
}
Algorithm
(cont)
input n
set factor to 2
while(some factor yet to try)
{
if (n is divisible by factor)
{
output factor
set n to n / factor
}
}
Algorithm
(cont)
input n
set factor to 2
while(some factor yet to try)
{
if (n is divisible by factor)
{
output factor
set n to n / factor
}
else
{
increment factor
}
}
Algorithm (cont)
input n
Why not?
set factor to 2
while(some factor yet to try) while(some factor yet to try)
{
{
if (n is divisible by factor)
if (n is divisible by factor)
{
{
output factor
output factor
set n to n / factor
set n to n / factor
}
}
else
increment factor
{
}
increment factor
}
}
Program
#include <stdio.h>
/* Print out the prime factors of a number */
int main()
{
int n, factor ;
return 0;
}
Program (cont)
#include <stdio.h>
/* Print out the prime factors of a number */
int main()
{
int n, factor ;
printf("\nEnter integer: ") ;
scanf("%d", &n) ;
return 0;
}
Program (cont)
#include <stdio.h>
/* Print out the prime factors of a number
*/
int main()
{
int n, factor ;
printf("\nEnter integer: ") ;
scanf("%d", &n) ;
printf("\nThe prime factors of
/*
Try each possible factor in turn
printf("\n\n");
return 0;
}
%d
are: ", n) ;
*/
/*
Try each possible factor in turn
factor = 2;
while ( factor <= n && n > 1 )
{
}
*/
/*
Try each possible factor in turn
*/
factor = 2;
while ( factor <= n && n > 1 )
{
if (n % factor == 0)
{
/* n is a multiple of factor,
** so print factor and divide n by factor */
printf(" %d", factor) ;
n = n / factor ;
}
}
/*
Try each possible factor in turn
*/
factor = 2;
while ( factor <= n && n > 1 )
{
if (n % factor == 0)
{
/* n is a multiple of factor,
** so print factor and divide n by factor */
printf(" %d", factor) ;
n = n / factor ;
}
else
{
/*
**
n is not a multiple of factor;
try next possible factor */
factor++ ;
}
}
/*
Try each possible factor in turn
*/
factor = 2;
while ( factor <= n && n > 1 )
{
if (n % factor == 0)
{
/* n is a multiple of factor,
** so print factor and divide n by factor */
printf(" %d", factor) ;
n = n / factor ;
}
else
{
/*
**
n is not a multiple of factor;
try next possible factor */
factor++ ;
}
}
#include
<stdio.h>
/* Print out the prime factors of a number
*/
int main()
{
int n, factor ;
printf("\nEnter integer: ") ;
scanf("%d", &n) ;
printf("\nThe prime factors of
/*
%d
Try each possible factor in turn
are: ", n) ;
*/
factor = 2;
while ( factor <= n && n > 1 )
{
if (n % factor == 0)
{
/* n is a multiple of factor,
** so print factor and divide n by factor. */
printf(" %d", factor) ;
n = n / factor ;
}
else
{
/*
**
n is not a multiple of factor;
try next possible factor */
factor++ ;
}
}
printf("\n\n");
return 0;
}
factor1.c
/*
Try each possible factor in turn
*/
factor = 2;
while ( factor <= n && n > 1 )
{
if (n % factor == 0)
Change from
{
/* n is a multiplewhile-loop
of factor,to for** so print factor and divide
loop? n by factor */
printf(" %d", factor) ;
n = n / factor ;
}
else
{
/*
**
n is not a multiple of factor;
try next possible factor */
factor++ ;
}
}
/*
Try each possible factor in turn
*/
for ( factor = 2; factor <= n && n > 1 ; )
{
if (n % factor == 0)
{
/* n is a multiple of factor,
** so print factor and divide n by factor */
printf(" %d", factor) ;
n = n / factor ;
}
else
{
/*
**
n is not a multiple of factor;
try next possible factor */
factor++ ;
}
}
#include
<stdio.h>
/* Print out the prime factors of a number.
*/
int main()
{
int n, factor ;
printf("\nEnter integer: ") ;
scanf("%d", &n) ;
printf("\nThe prime factors of
/*
%d
are: ", n) ;
Try each possible factor in turn.
*/
for ( factor = 2; factor <= n && n > 1 ; )
{
if (n % factor == 0)
{
/* n is a multiple of factor,
** so print factor and divide n by factor. */
printf(" %d", factor) ;
n = n / factor ;
}
else
{
/*
**
n is not a multiple of factor;
try next possible factor. */
factor++ ;
}
}
printf("\n\n");
return 0;
}
factor2.c