CS192 Lecture 7: Arithmetic, Precedence, Conversions, and Relational & Logical Operators, Slides of Computer Programming

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Lecture 07

1

CS 192Lecture 7Fall 2011

October 5, 2011Ghufran Ahmed

Lecture 07

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Arithmetic Operators

-^

Increment and decrement operators

-^

x = x + 1;

Or

++x;

Or

x++;

(Prefix and postfix)

-^

x = x – 1;

Or

--x;

Or

x--;

-^

SubtletiesExample:

int x=5, y=5;cout << x++ << endl;cout << ++y << endl;cout << x << ‘,’ << y;

-^

x = 10;y = ++x;

-^

x = 10;y = x++;

Lecture 07

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Operator Precedence & Associativity•^

Precedence:

If two operators apply to same

operand, higher precedence operator appliedfirste.g. (3 + 5 * 6) has value 33

-^

Associativity:

If two operators have same

precedence, associate L-R or R-L as definede.g. (120 / 6 * 5) has value 100 as associatefrom L-R

Lecture 07

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Evaluation Order of Operators

Precedence of Arithmetic and

Assignment Operators

Precedence

Operator

Associativity

1

Parentheses:

( )

Innermost first

2

Unary operators^ ++ --+ -

(unary)

Right to left

3

Binary operators *** / %**

Left to right

4

Binary operators + -

Left to right

5

Assignment operators *= += -= = /= %=

Right to left

Lecture 07

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Type Conversions on Assignment

-^

Type converted to that of the receiving variable float

tree

=

3;

//int

to

float

int

guess

=

3.9832;

//float

to

int

int

debt

=

3.0E12;

//erroneous

-^

What output if we

cout tree

,^

guess

and

debt

?

-^

Potential problems: Loss of precision, or loss offractional part, or out of range. Compilercomplains usually

Lecture 07

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Casting

• A programmer forces an expression to be of

the specified type (as opposed to automaticconversions)

(type) expression

or

type (expression)

e.g.

(float) 5/2; char(77);

long (shorty); int (‘Z’);

Lecture 07

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Relational & Logical Operators

• Relational for comparison and Logical for

connecting

true

and

false

values

• Outcome of a relational or logical expression

is

bool

(true or false)

• For relational operators, operands and

expressions of any data type that can becompared

• Any non-zero value converted to

true

, zero to

false

Lecture 07

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Relational & Logical Operators

-^

Fill table of (p AND q), (p OR q), (NOT p). Also for 3variables. Precedence lower than arithmetic operators #include <iostream.h>int main(){

int p, q;cout << "Enter P (0 or 1): ";cin >> p;cout << "Enter Q (0 or 1): ";cin >> q;cout << "P AND Q: " << (p && q) << endl;cout << "P OR Q: " << (p || q) << endl;return 0; }

Lecture 07

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Relational & Logical Operators

• Pitfall: Do not use strings of inequalities. They

may be legal C++ code but will not do whatyou (for now) expect them to do if (x < y < z)

// WRONG!

cout << "y is between x and z“ << endl;

• Instead, you have to write: if ((x < y) && (y < z)) // CORRECT!

cout << "y is between x and z" << endl;

Lecture 07

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sizeof operator

sizeof

operator to test sizes

e.g.

cout << sizeof(int);cout << sizeof i; //i is a variable