1. Chapter 6 Decision Making and Looping
PROGRAMMING IN ANSI C

2. Let's find out the law of such question:
12/2/2018
Question
Questions:
How do we calculate the sum from 1 to 5?
How do we calculate the sum from 1 to 100?
main()
{ int sum=0;
sum=sum+1;
sum=sum+2;
sum=sum+3; ……
sum=sum+100;
printf("sum=%d",sum); }
main()
{ int sum=0;
sum=sum+1;
sum=sum+2;
sum=sum+3;
sum=sum+4;
sum=sum+5;
printf("sum=%d",sum); }
Let's find out the law of such question:
When i=1,2,3,…,100
do: sum = sum + i;
Loop construct!

3. 12/2/2018
Flow chart
In a looping, a sequence of statements is repetitively executed until the loop test condition can’t be satisfied.
A loop statement consists of 2 segments:
The loop control statement
The loop body
end
begin
i=1, sum=0;
i<=100 Y N
i=i+1;
output: sum
sum = sum+i;

4. Chapter 6 In this chapter, we will learn: while statement
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Chapter 6
In this chapter, we will learn:
while statement
do...while statement
for statement
Assisted control statements: break and continue
Looping consists of if and goto

5. 12/2/2018
while Statement
The form of while statement: while ( test condition ) loop body
test condition
loop body
true (not 0)
false (0)
The test condition is evaluated first, and if it is true, the loop body is executed.

6. 12/2/2018
while Statement
If the loop body consists of more than one statement, we should use compound statement.
Program to calculate the sum from 1 to 100.
end
begin
i=1, sum=0;
i<=100 Y N
i=i+1;
output: sum
sum = sum+i;
main() {
int i=1, sum=0;
while ( i <= 100 )
{ sum = sum + i;
i++; }
printf("%d", sum);
test condition
loop body

7. while Statement Program to calculate the sum from 1 to 100.
12/2/2018
while Statement
Program to calculate the sum from 1 to 100.
We can use ctrl+break to stop the execution of program.
infinite loop
end
begin
i=1, sum=0;
i<=100 Y N
i=i+1;
output: sum
sum = sum+i;
main() {
int i=1, sum=0;
while ( i <= 100 )
sum = sum + i;
i++;
printf("%d", sum); }
main() {
int i=1, sum=0;
while ( i <= 100 )
{ sum = sum + i;
i++; }
printf("%d", sum);

8. while Statement – 2 Segments
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while Statement – 2 Segments
while ( test condition )
loop body
if (sum==50)
printf("i=%d",i);
{ sum = sum+i;
i = i+1; }
printf("sum=%d", sum=sum+i); ;
statment type
examples
expression statement
printf("sum=%d", sum=sum+i);
void statement ;
control statement
if (sum==50) printf("i=%d",i);
compound statement
{ sum=sum+i; i=i+1; }

9. while Statement – 2 Segments
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while Statement – 2 Segments
The loop body can be any type statement.
The loop body should be a single statement or a compound statement.
The loop body must contain some statements making the loop tend to end. Avoid infinite loop.
while ( test condition )
loop body

10. 12/2/2018
do...while Statement
The form of do...while statement: do loop body while ( test condition );
test condition
loop body
true
false
The loop body is executed first, and then the test condition is evaluated.
In do...while statement, the loop body is always executed at least once.

11. 12/2/2018
do...while Statement
do...while statement can change to while statement:
test condition
loop body
true
false
loop body
test condition
loop body
true
false

12. 12/2/2018
do...while Statement
do...while statement can change to while statement:
do loop body while ( test condition );
loop body while ( test condition )
loop body

13. 12/2/2018
do...while Statement
Like while statement, if the loop body consists of more than one statement, we should use compound statement.
Program to calculate the sum from 1 to 100.
end
begin
i=1, sum=0;
i<=100 Y N
i=i+1;
output: sum
sum = sum+i;
main()
{ int i=1, sum=0; do
{ sum=sum+i;
i++; }
while ( i <= 100 );
printf("%d",sum);
loop body
test
condition

14. do...while Statement – 2 Segments
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do...while Statement – 2 Segments do
loop body
while ( test condition );
The loop body can be any type statement.
The loop body should be a single statement or a compound statement.
The loop body must contain some statements makeing the loop tend to end. Avoid infinite loop.
Pay attention to this semicolon!

15. while & do...while Statement
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while & do...while Statement
Compare while with do...while statement.
101 1
5050 1
5050
101
101
main()
{ int i, sum=0;
scanf ( "%d", &i );
while ( i <= 100 ) {
sum = sum + i;
i++; }
printf ( "%d", sum );
main()
{ int i, sum=0;
scanf ( "%d", &i ); do {
sum = sum + i;
i++;
} while ( i <= 100 );
printf ( "%d", sum ); }
while —— the test condition is evaluated first do...while —— the loop body is evaluated first
while —— the times of execution of loop body≥0 do……while —— the times of execution of loop body≥1

16. 12/2/2018
for Statement
exp2
exp1
true
false
loop body
exp3
The form of for statement: for ( [exp1]; [exp2]; [exp3] ) loop body
exp1, exp2 and exp3 are any type expressions, and they all can be omitted. But the separator semicolon can't be omitted.
for ( ; ; ) is equivalent to while (1) – infinite loop
for statement can be changed to while statement

17. 12/2/2018
for Statement
The form of for statement: for ( [exp1]; [exp2]; [exp3] ) loop body
The general application form of for statement：
for ( initialization; test condition; increment )
loop body
e.g. for( sum = 0, i = 1; i <= 100; i ++ ) sum = sum + i;
is equivalent to：
sum = 0;
i = 1;
while ( i <= 100 )
{ sum = sum + i;
i ++; }

18. 12/2/2018
for Statement
The form of for statement: for ( [exp1]; [exp2]; [exp3] ) loop body
exp1 and exp3 can be comma expression.
e.g. for( sum = 0, i = 1; i <= 100; sum += i, i++ );
is equivalent to：
sum = 0;
for( i = 1; i <= 100; i++ ) sum += i;

19. for Statement Program to calculate the sum from 1 to 100. main()
12/2/2018
for Statement
Program to calculate the sum from 1 to 100.
end
begin
i=1, sum=0;
i<=100 Y N
i=i+1;
output: sum
sum = sum+i;
main()
{ int i, sum;
sum = 0;
for ( i = 1; i <= 100; i++ ) sum = sum + i;
printf ( "%d", sum ); }
i = 1;
for ( ; i <= 100; )
{ sum = sum + i;
i++; }
for ( i = 1; i <= 100 ; sum += i, i++ );
i = 1;
for ( ; i <= 100; i++ )
sum = sum + i;

20. O Nesting of Loops external loop
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Nesting of Loops
external loop
Nesting of loops means: A loop body contains another complete loop construct.
These 3 loop constructs can nest each other, without limitation of the layers.
for ( ; ; ) { …… do
while()
} while ( ); }
…...
for ( ; ; ) { …… do
} while ( );
while() }
…... O
while ( ) { …… do
} while ( );
…... }
while ( ) { …… }
…... do { ……
} while ( );
…...
internal loop

21. 12/2/2018
break Statement
Form: break;
Function:
Exit from the loop containing it, causing this loop to be terminated.
Exit form the switch statement containing it, causing this switch statement to be terminated.
One break can exit only one single loop, the nearest loop.
The break can only be used in a loop or a switch statement.

22. break Statement break; for while do exp1 false false exp exp2 …… true
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break Statement
break;
exp2 ……
break;
false
true
for
exp1
exp3
false
exp ……
break;
true
while do ……
break;
exp
false
true
while

23. break Statement Program to calculate the sum from 1 to 100. main() {
12/2/2018
break Statement
Program to calculate the sum from 1 to 100.
end
begin
i=1, sum=0;
i<=100 Y N
i=i+1;
output: sum
sum = sum+i;
main() {
int i, sum = 0;
for ( i = 1; ; i++ )
{ if ( i > 100 )
break;
sum = sum + i; }
printf ( "%d", sum );
i = 1;
for ( ; ; )
{ if ( i > 100 )
break;
sum = sum + ( i++ ); }

24. continue Statement Form: continue; Function:
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continue Statement
Form: continue;
Function:
Skip the following statements in this loop, causing the test condition of the next loop to be judged.
The continue can only be used in loops.

25. continue Statement continue; exp2 …… continue; …... false true for
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continue Statement
exp2 ……
continue;
…...
false
true
for
exp1
exp3
continue;
true
exp
false
while ……
continue;
false
true do ……
continue;…...
exp
while

26. 12/2/2018
continue Statement
Output the numbers, between 100 and 200, which can't be divided exactly by 3.
main() {
int n;
for ( n = 100; n <= 200; n++ )
{ if ( n % 3 == 0)
continue;
printf ( "%5d", n ); }

27. 12/2/2018
Loops – Program 1
Output the former 40 numbers of the Fibonacci sequence.
Fibonacci sequence: 1, 1, 2, 3, 5, 8, 13, 21, 34, …… F1 = (n = 1) F2 = (n = 2) Fn = Fn-1 + Fn-2 (n≥3)
f1 = 1, f2 = 1
for i = 1 to 20
Output: f1, f2
f1 = f1 + f2
f2 = f2 + f1
f1 f2 ? ? ? f2 f1
f1…

28. Loops – Program 1 main() { long f1 = 1, f2 = 1; int i;
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Loops – Program 1
main()
{ long f1 = 1, f2 = 1;
int i;
for ( i = 1; i <= 20; i++ )
{ printf ( "%12ld %12ld", f1, f2 );
if ( i % 2 == 0 )
printf ( "\n" );
f1 = f1 + f2;
f2 = f2 + f1; }
i=1;
while ( i <= 20 )
{ printf ( "%12ld %12ld", f1, f2 );
if ( i % 2 == 0 ) printf( "\n" );
f1 = f1 + f2;
f2 = f2 + f1;
i ++; }
i=1; do
{ printf ( "%12ld %12ld", f1, f2 );
if ( i % 2 == 0 ) printf ( "\n" );
f1 = f1 + f2;
f2 = f2 + f1;
i ++;
} while ( i <= 20 );

29. Loops – Program 2 Judge whether an integer is a prime number or not.
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Loops – Program 2
Judge whether an integer is a prime number or not.
Make m be divided by all the numbers between 2 and the square root of m.
If m can be divided exactly by a certain number in those, m is not a prime number, otherwise it is.
Read in m
i=2
when i ≤ k
m%i==0?
true
false
break;
i = i + 1
i > k
m is a prime
m isn't a prime
k = (int) sqrt(m)

30. 12/2/2018
If m can be divided exactly by the number between 2 and sqrt(m), m is not a prime number, so the loop will be terminated by break statement, and at that time, i must be less or equal to k.
Otherwise m is a prime number, and after the last loop, i is equal to k+1.
Loops – Program 2
#include <math.h>
main()
{ int m, i, k;
scanf ( "%d", &m );
k = sqrt ( m );
for ( i = 2; i <= k; i++ )
if ( m % i == 0 ) break;
if ( i > k )
printf( "%d is a prime number.", m);
else
printf( "%d is not a prime number.", m); }

31. Loops – Program 2 #include <math.h> main() { int m, i, k;
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Loops – Program 2
#include <math.h>
main()
{ int m, i, k;
scanf ( "%d", &m );
k = sqrt ( m );
i = 2;
while ( i <= k )
{ if( m % i == 0 ) break;
i ++; }
if ( i > k ) printf( "%d is a prime number.", m);
else printf( "%d is not a prime number.", m); }
Can't judge 1, 2, 3 !
for ( i = 2; i <= k; i++ )
if ( m % i == 0 )
{ printf ( "%d is not a prime number", m );
break; }
else if ( i == k )
printf ( "%d is a prime number", m ); do
{ if( m % i == 0 ) break;
i ++; } while ( i <= k );

32. Loops – Program 3 Output all the primes between 100 and 200.
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Loops – Program 3
Output all the primes between 100 and 200.
Try to use while and do…while statement to rewrite this program.
#include <math.h>
main()
{ int m, i, k, n = 0;
for ( m = 101; m <= 200; m = m + 2 )
{ k = sqrt ( m );
for ( i = 2; i <= k; i++ )
if ( m % i == 0 ) break;
if ( i > k ) { printf ( "%5d", m );
n = n + 1; }
if ( n % 10 == 0) printf ( "\n" ); }

33. 12/2/2018
Loops – Program 4
Read in a positive integer, and output it in reversed order. For example: read in 12345, output
#include <math.h>
main()
{ int n;
printf ( "Input a positive integer:" );
scanf ( "%d", &n );
while ( n != 0 )
{ printf ( "%d", n % 10 );
n = n / 10; /* number is decreased by 10 times */ }

34. Loops – Program 5 Output the multiplication table.
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Loops – Program 5
Output the multiplication table.
"i" represents the line： （1≤i≤9）
"j" represents the column： （1≤j≤i） j i ……
5×5＝25
5×4＝20
5×3＝15
5×2＝10
5×1＝5
4×4＝16
4×3＝12
4×2＝8
4×1＝4
3×3＝9
3×2＝6
3×1＝3
2×2＝4
2×1＝2
1×1＝1 ……
5×5＝25
5×4＝20
5×3＝15
5×2＝10
5×1＝5
4×4＝16
4×3＝12
4×2＝8
4×1＝4
3×3＝9
3×2＝6
3×1＝3
2×2＝4
2×1＝2
1×1＝1

35. Loops – Program 5 main() { int i, j; for ( i = 1; i < 10; i++ )
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Loops – Program 5
main() {
int i, j;
for ( i = 1; i < 10; i++ )
for ( j = 1; j <= i; j++ )
printf ( "%d*%d=%d\t", j, i, i*j ); }
printf ( "\n" );
Try to use other nesting of loops to rewrite this program.

36. Loops – Program 6 Please input a number: Please input a number:
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Loops – Program 6
Please input a number:
Please input a number:
Read in integer n, and output n factorial (n!). 8 5
8!=-25216
5!=120
8!=40320
0!=120
main()
{ int n; int m=1;
printf ( "Please input a number:" );
scanf ( "%d", &n );
while ( n >= 1 )
{ m *= n;
n -- ; }
printf ( "%d!=%d", n, m );
long
printf ( "%d!=", n );
printf ( "%d", m );
printf ( "%ld", m );

37. 12/2/2018
goto Statement
Used to: Jump unconditionally from one point to another in a program.
General forms: goto label; label: statement; …… or …… label: statement; goto label; …… ……

38. goto Statement About label:
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goto Statement
About label:
A label must be a valid identifier, don’t use an integer as a label.
A label can only mark executable statement, and can’t mark declaration statement.
A label is unique in a function. Don’t use the same label to mark different statements.

39. if and goto Program to calculate the sum from 1 to 100. main() {
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if and goto
Program to calculate the sum from 1 to 100.
end
begin
i=1, sum=0;
i<=100 Y N
i=i+1;
output: sum
sum = sum+i;
main() {
int i=1, sum=0;
loop: if ( i <= 100 )
sum += i;
i++;
goto loop; }
printf ( "%d", sum );

40. goto Statement goto Statement can: Form looping with if statement;
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goto Statement
goto Statement can:
Form looping with if statement;
Jump out of looping.
while()
{ …… {
goto label； …… }
label： statement

41. goto Statement It is a good practice to avoid using goto statement!
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goto Statement
It is a good practice to avoid using goto statement!
goto statements:
Making the compiler generate less efficient code;
Making the program logic more complicated;
Making the program more unreadable;
Even breaking down the whole system.

42. Homework Review Questions P174
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Homework
Review Questions P174
6.1, 6.2, 6.9, 6.11～6.13, 6.14(a) (Write down in your exercise book.)
Programming Exercises