1. By C. Shing ITEC Dept Radford University
Chapter 3 Flow Control
By C. Shing
ITEC Dept
Radford University

2. Objectives Understand how to use assignment statement
Understand how to use conditional statement
Understand how to use loop statement

3. Assignment Statement Identifier assignment_operator expression;
Represents
identifier = identifier assignment_operator
(expression);
After evaluating the right hand side of =,
it stores result to the left hand side identifier
(i.e. memory) and change to the data type of left
hand side

4. Assignment Statement – assignment operator
=, +=,-=, *=, /=, %=
Example:
x *= 3
Means x=x*3

5. Assignment Statement (Cont.)
Identifier = expression;
Both sides of data type should match. If not, then
the right hand side of type will be widened
automatically to the left hand side data type.
Otherwise, warning message will be given
for narrowing data type.

6. Assignment Statement (Cont.)
Type conversion:
Automatic conversion rule
Manual conversion: use casting

7. Assignment Statement (Cont.)
Automatic conversion rule:
The widest data type in an expression determines the
data type of the expression
unsigned type is wider than the corresponding type
the rest from widest: double, float, long, int, short (or char)
Finally, the expression data type will be widened to
the data type of the identifier

8. Assignment Statement (Cont.)
Examples:
unsigned u;
long g;
int i;
unsigned long ul;
ul = u-3*g +i; // right hand side result type
// long is converted to unsigned long
// before stored in ul

9. Assignment Statement (Cont.)
Examples:
unsigned u;
float f;
int i;
double db;
db = u/3-i+f; // right hand side result type
// float is converted to double before
// stored to db

10. Assignment Statement (Cont.)
Casting:
Identifier = (left hand side type) (expression)

11. Assignment Statement (Cont.)
Examples:
unsigned u;
long g;
int i;
unsigned long ul;
i = (int) (u-3*g +4); // right hand side result type
// is long

12. Conditional Statement - if
if, if .. else, ?:, switch
if form:
if (condition) { … }

13. Conditional Statement – if (Cont.)
Note: condition is evaluated using short-circuit
If condition consists of condition1 and condition2
connected by a logic operator:
Condition1 && condition2
if condition1 is false,
then it will not evaluate condition2
Condition1 || condition2
if condition1 is true,

14. Conditional Statement – if (Cont.)
Example:
int x;
if (x = 5) {
printf(“Always TRUE is printed!\n”); }

15. Conditional Statement – if … else
if … else form:
if (condition) { … }
else

16. Conditional Statement – if … else (Cont.)
Example:
if (x<y) {
min = x; }
else
min = y;

17. Conditional Statement – ?:
form: identifier =
(condition)?true part:false part

18. Conditional Statement – ?: (Cont.)
Example: (Same example as previous one)
min = (x<y) ? x : y;

19. Conditional Statement – switch
switch form: values (char/int) cannot be range as in
Visual Basic
switch (expression) {
case value1: …
break; // quit the current (switch) statement
case value2:
case value3:
break; // do this part when value2 or value3

20. Conditional Statement – switch (Cont.)
switch form: (Cont.)
case …: …
break;
default: // everything else }

21. Conditional Statement – switch (Cont.)
Example:
switch (character) {
case ‘a’:
case ‘A’: a_count++;
break; …
default:
printf(“%c is not a letter!\n”, character); }

22. Loop Statement while do … while for Steps of writing a loop:
Identify the loop body: repetition part
Identify condition that can make the
repetition of loop body either true of false;
Make sure the first time, condition is true
Initialize loop condition before loop
Update loop condition at end of loop body

23. Loop Statement - while while form: repeat loop body when condition is
true – pre-condition
while (condition part) { … }
Note: condition part can be more than one statement,
separated by a comma
Example: while (scanf("%c", &character), character !='\n');
What task does the statement above perform?

24. Loop Statement - while Condition can be Example: int count=1;
Counter control (definite loop): use counter
Example:
int count=1;
// the following prints out 5 times only
while (count <= 5) {
++count;
printf(“%d\n”, count); }

25. Loop Statement - while Condition can be (Cont.)
Sentinel control (indefinite loop):
use pseudo data (sentinel) for condition
Example: sentinel data is any negative score
int score;
scanf(“%d”, &score);
while (score >= 0) {
printf(“%d\n”, score); }
Yard-Meter Conversion

26. Loop Statement - while Condition can be (Cont.) Example: Skip 1st Line
More than 1 statement
Example:
Skip 1st Line

27. Loop Statement – while (Cont.)
Example:
Hard –to-find Error:
int x;
// the following is an infinite loop
while (x = 5) {
printf(“Always TRUE is printed!\n”); }

28. Loop Statement – while (Cont.)
Example: (Use break to get out of loop)
int x, count=0;
// the following prints out TRUE 5 times only
while (x = 5) {
++count;
printf(“Always TRUE is printed!\n”);
if (count == 5)
break; }

29. Loop Statement – do while
do while form: repeat loop body when condition
is true – post-condition do { …
} while (condition);

30. Loop Statement – do while (Cont.)
Example:
int x=0; do {
++x;
printf(“Always TRUE is printed!\n”);
} while (x != 5)

31. Loop Statement - for for form: repeat loop body when condition is
true – pre-condition
Most general form: can represent
while and do while loops

32. Loop Statement – for (Cont.)
for (initialization, exprPart1, …;
exprPart2, …,condition;
exprPart3, …,last statement in loop body) { … }

33. Loop Statement – for (Cont.)
Example:
int i; // loop index must be defined
// outside for loop
for (i=0;i<5;++i) {
printf(“TRUE is printed!\n”); // print 5 times }

34. Loop Statement – for (Cont.)
Example: (Same as the previous one)
int i=0;
// print 5 times
for (;i<5; printf(“TRUE is printed!\n”), ++i);

35. Loop Statement – for (Cont.)
Example: (Use continue statement to skip current loop)
int x, count=0;
// the following prints out TRUE 5 times only
while (count <=10) {
++count;
if (count %2 == 1) // skip odd number times of print
continue;
printf(“TRUE is printed!\n”); }

36. Loop Statement – for (Cont.)
Represent while loop:
for (;condition;) { … }

37. Loop Statement – for (Cont.)
How to check end of file:
If read a character: (Must deal with \n)
Use scanf(“%c”, &c)>0 to read
in a character to check any character being read
(if reach to end of file, scanf returns -1)
Example 1: a.out < checkEOF.c
If read an integer:
Use scanf(“%d”, &number)>0 to read

38. Loop Statement – for (Cont.)
Represent do while loop:
for (;loop body statements, condition;);

39. Keyboard Input Format Function - scanf
Form: scanf(“pure_format”, variable_address);
Format: similar to those used in printf, however, no character or strings
included
%i: for decimal, octal (data begins with 0) or hexadecimal (data begins with 0x)
If use %s format, it reads all until it reaches the first white space
&variable represents the address of the memory (or variable)
Example:
char c;
int i;
double db;
char s[80]; // remember s is address: array of 80 characters
scanf(“%c%d%lf%s”, &c, &i, &db, s);
// sample data:a This is a sample data
// c=‘a’, i=100, db=-1.23, s=“This”

40. Class Example Example 1 Example 2 : print character ‘2’
in front of each line
Read Character : read a character after reading a
number
For loop

41. Assignment
Assignment #1

42. Practice Given int a=1,b=2,c=3,d=4;
Find the values of the following table:
Expression Value
________ _____
a +=b+c a=
b *=c=d+5 b=

43. Practice - Answer Given int a=1,b=2,c=3,d=4;
Find the values of the following table:
Expression Value
________ _____
a +=b+c a= 6
b *=c=d+5 b= 18

44. References Herbert Schildt: C: The Complete Reference,
4th ed, Osborne Publishing
Deitel & Deitel: C How to Program, 4th ed.,
Chapter 3, 4 & 9, Prentice Hall