1. Chapter 3 Operators and Expressions
PROGRAMMING IN ANSI C

2. Operators Arithmetic + - * / % ++ -- Relational
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Operators
Arithmetic
* / %
Relational
< <= > >= == !=
Logical
！ && ||
Bitwise
<< >> ~ | ^ &
Assignment
= (Shorthand Assignment: += -= etc.)
Comma ,
Explicit conversion
(type)
Conditional ?:
Arrow
->
Pointer
* &
Array element
[ ]
Number of bytes
sizeof
others
( ) - .

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Expressions
An expression is a sequence of operands and operators that produces a single value.
This value may be any data type except void.

4. How to learn operators and expressions?
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How to learn operators and expressions?
When we study operators and expressions, we must pay attention to such 5 points:
The function of operators.
The relation of operators and operands:
How many operands does the operator need?
Which types does the operator require?
The precedence of the operator.
The associativity of the operator.
The type of the calculated result.

5. Arithmetic Operators & Expressions
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Arithmetic Operators & Expressions
5 % 2 =
-5 % 2 =
5 % -2 =
-5 % -2 =
5 % 1 =
5 % 1.0 =
5 / - 2 =
5 / =
+：Addition or unary plus e.g. 3+2，+3.5
- ：Subtraction or unary minus e.g. 3-2，-3.5
* ：Multiplication e.g. 3*2，3.5*2
/ ：Division e.g. 3/2，3.5/2
If the 2 operands both are integers, the result is an integer and its fractional part is truncated. e.g. 8/5=1
% ：Modulo division e.g. 5%2 = 1
Both of the 2 operands must be integers .
The sign of the result is the same as the dividend. 1
- 1 1
- 1 O
- 2
- 2.5

6. Arithmetic Operators & Expressions
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Arithmetic Operators & Expressions
+，-，*，/，%
Precedence: (Unary) higher than * / % higher than + -
Associativity：+，- (Unary): Right to left others：Left to right

7. Arithmetic Operators & Expressions
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Arithmetic Operators & Expressions
Notice：
If the operands are all integers, the result must be an integer.
If one of the operands is a real number, the result must be a real number.
The modulo division operator cannot used on real numbers but only integers, and the sign of result is the same as the sign of dividend.

8. Arithmetic Operators & Expressions
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Arithmetic Operators & Expressions
An arithmetic expression is a combination of variables, constants, and operators arranged as per the syntax of the language. e.g. a * b / c – ( 'f') * (5 % 3)

9. Arithmetic Operators & Expressions
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Arithmetic Operators & Expressions
You must pay attention to :
The expression “a multiplied by b” must be written to “a*b” but not “ab”;
C doesn’t supply exponential operator, so you can write some multiplication, or you can use mathematic function pow(x,y) in the C function library to express xy;
Notice the precedence of those arithmetic operators, and you should reasonably use parentheses.

10. Arithmetic Operators & Expressions
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Arithmetic Operators & Expressions
When expressions include real values, then it is important to take necessary precautions to guard against certain computational errors. e. g. a = 1/3.0; b = a * 3.0;
Don’t make any expression divide zero.
Avoid data overflow.

11. Relational Operators & Expressions
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Relational Operators & Expressions
< <= > >= == !=
Value of Relational Expression: 1(True) & 0(False)
Precedence： < <= > >= higher than == != Arithmetic operators higher than relational operators.
Associativity：Left to right
Relational operators are used in the test condition of decision or loop statements to decide the course of action of running program.

12. Relational Operators & Expressions
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Relational Operators & Expressions
int a=3, b=2, c=1, d, f;
a > b
c == a > b
a < b + c
d = a > b
f = a > b > c
3>2，the value is 1
1==1， the value is 1
b+c=3， the value is 0
d=1
a>b is 1，1>c is 0，so: f = 0

13. Relational Operators & Expressions
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Relational Operators & Expressions
Notice
Avoid carrying out “==” and “!=” between real numbers. e.g / 3.0 * 3.0 == 1.0 /*not always 1 */ fabs ( 1.0 / 3.0 * ) < 1e-6
Pay attention to distinguish “=” and “==”. e.g. int a = 3, b = 2; a = b == a; /* a = 0 */

14. Logical Operators & Expressions
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Logical Operators & Expressions
! && ||
Precedence： ! higher than relational operators higher than && higher than ||
Associativity： ! ： Right to left && , ||: Left to right
Value of logical Expression: 1(True) & 0(False)
Operands: 0 denotes false, others denote true. e.g && 0 a b !a
a&&b
a||b 1

15. Logical Operators & Expressions
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Logical Operators & Expressions
int a = 4, b = 5; !a
a&&b
a||b
!a||b
4&&0||2
5>3&&0||8<4-!0
'c'&&'d'
!4 => 0
4 && 5 => 1
4 || 5 => 1
0 || 5 => 1
0 || 2 => 1
((5>3)&&0)||(8<(4-(!0))) = 0||0 => 0
, || 100 => 1

16. Logical Operators & Expressions
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Logical Operators & Expressions
Question：Write the expression of leap year. If the “year” is a leap year, it must satisfy one of the 2 conditions:
1) It can be divided exactly by 4, and it can’t be divided exactly by 100.
2) It can be divided exactly by 400.
( && )
year%4==0
year%100!=0 ||
year%400==0

17. Logical Operators & Expressions
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Logical Operators & Expressions
Short-circuit
When a logical expression is being evaluated, it is not each part linked by && or || all is evaluated. But only when it has to be evaluated, it is done.
a&&b /* Only when a is true, b is evaluated If a is false, b is not evaluated.*/
a||b /* Only when a is false, b is evaluated If a is true, b is not evaluated.*/ a=1; b=2; c=3; d=4; m=1; n=2;
( m = a >b ) && ( n = c > d );
/* m=0,n=2*/

18. Assignment Operators & Expressions
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Assignment Operators & Expressions =
Format：variable = expression
Precedence ： = lower than ||
Associativity： Right to left a = b = 5; int a = b = 5; Wrong! int a = 5, b = 5; Right!

19. Assignment Operators & Expressions
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Assignment Operators & Expressions
 c = 5, b = c, a = b /*a=5, b=5, c=5*/
 c = 6, a = 5+c /*a=11, c=6*/
 b = 4, c = 6, a = b+c /*a=10, b=4, c=6*/
int a, b, c;
a = b = c = 5;
a = 5 + (c=6);
a = (b=4) + (c=6);

20. Assignment Operators & Expressions
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Assignment Operators & Expressions
“shorthand ” assignment operators: +=, -=, *=, /=, %=
variable op = expression; is equivalent to: variable = variable op expression e.g. x * = y + 1; is equivalent to: x = x * (y + 1);

21. Assignment Operators & Expressions
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Assignment Operators & Expressions
int a = 2;
a += a -= a*a ;
 a += a –= 4
 a += (a = a – 4)
 a += (a = -2)
 a += a  a = a + a
 a = (-2) + (-2)  a = -4

22. Increment and Decrement Operators
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Increment and Decrement Operators
(10 / m) ++ Wrong! 10 / m ++ Right!
++ --
m ++; or m; is equivalent to: m = m + 1; m --; or m; is equivalent to: m = m - 1;
Precedence ： same as unary +, unary -, !
Associativity： Right to left

23. Increment and Decrement Operators
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Increment and Decrement Operators
int m=5, n; n = 10 / m++;
is equivalent to: n = 10/m; m++;
n = 10 / ++m;
is equivalent to: ++m; n = 10/m;

24. Increment and Decrement Operators
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Increment and Decrement Operators
j=3; k=++j;
j=3; k=j++;
j=3; printf("%d",++j);
j=3; printf("%d",j++);
a=3;b=5;c=(++a)*b;
a=3;b=5;c=(a++)*b;
j=j+1; k=j; result：k=4, j=4
k=j; j=j+1; result ：k=3, j=4
 j=j+1; printf(); output:4
 printf(); j=j+1; output:3
 a=a+1; c=a*b; result ：a=4，c=20
 c=a*b; a=a+1; result ：a=4，c=15

25. Increment and Decrement Operators
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Increment and Decrement Operators
Notice
The operand of ++ or -- must be a variable and not any expression or any constant.

26. Comma Operator & Expressions
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Comma Operator & Expressions
expression 1, expression 2, ……, expression n
Value of Relational Expression: the value of expression n.
Precedence ： the lowest
Associativity： Left to right

27. Comma Operator & Expressions
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Comma Operator & Expressions
a = 3*4, 5*2 ;
b = (a = 3*4, 5*2) ;
a=1; b=2; c=3;
printf("%d,%d,%d", a, b, c);
printf("%d,%d,%d", (a, b, c), b, c);
a = 12
a = 12, b = 10
output: 1, 2, 3
output: 3, 2, 3

28. Implicit Type Conversion
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Implicit Type Conversion
short & char
int
unsigned int
long
unsigned long
float
double
long double
The rules of conversion: P70 In all expressions except assignments, any implicit type conversions are made from a lower size type to a higher size type as shown here:

29. Implicit Type Conversion
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Implicit Type Conversion
During assignment:
If expression is real type and the variable is integer type, the value of expression will be truncated its fractional part.
If expression is double type and the variable is float type, the value of expression will be round its digits.
If expression is long type and the variable is int type, the value of expression will be drop its higher byte.

30. Implicit Type Conversion
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Implicit Type Conversion
int i, x; float f; double d; long L;
x = L / i i * f d;
long
float
double
Notice: in the whole process of type conversion, only the type of the interim value used in evaluation is converted, but all the types of variables are not converted. Except the variable “x” assigned a value, all the values of other variables are not changed.
float
float
double
int
double

31. Explicit Type Conversion
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Explicit Type Conversion
Form ：(type-name) expression
Precedence ： same as unary +, unary -, !, ++, --
Associativity： Right to left
e.g. (int) (x+y)  (int) x + y
Notice: like the implicit type conversion, only the type of the interim value used in evaluation is converted, but all the types of variables are not converted. Of course, the values of these variables are not changed.
main() {
float x, y ;
x = 3.6 ;
y = (int) x * 2 ;
printf("x=%.2f, y=%.2f", x, y); }
x=3.60, y=6.00

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Homework
Review Questions P78 3.1~3.8 & 3.10 write down in your exercise book
Programming Exercises