Arithmetic Expressions

- how to write arithmetic expressions on double and int data types

- arithmetic operators: +, -, *, /, % (remainder)

o division with 0 is undefined (causing run-time error)

o m = (m/n)*n + m%n

- data type of an expression

o x+y is int if both x and y are int

o x+y is double is either x or y are double (this includes mixed type expressions)

- how assignment works

o assign statement is executed according to the mixed-type rules

o the result is stored in the variable on the left

e.g. y = m/n; if y is int type, only integral part of division m/n is saved

- Type casts

o if m and n are int type (e.g. m = 5, n = 2), the value of y after the statement y = m/n is 2, even if y is of double type!

o To prevent such behavior, type casts are used:

y = (double) m / (double) n; or,

y = (double) m / n;

- + and - can be unary or binary operators

o x = -y; /* unary */

o z = y - x; /* binary */

- Rules for evaluating expressions:

o Parenthesis rule (executed from the inside out)

o Operator precedence:

§ unary +, -

§ *, /, %

§ binary +, -

o Associativity: evaluate operators of the same precedence from left to right

§ x * y * z + a / b – c * d = (x*y*z) + (a/b) – (c*d)

o look at examples from Table 2.10 in the textbook

Formatting Numbers in Program Output

- read section 2.6 from the textbook

- pay attention to Tables 2.11, 2.12, 2.13

Interactive Mode

- Two modes of computer operation:

o interactive: interacts with user (like in Lab 1 assignment)

o batch: scans data from a file

- Input redirection:

o “conversion <mydata” uses data from file “mydata”as input

o note: in this case, there is no need for printf prompt to user to enter data

- Output redirection

o “conversion <mydata >myoutput” also outputs the results to file “myoutput”

Common Programing Errors

- Syntax errors – compiler cannot translate it. Typical errors:

o missing semicolomn

o undeclared variable

o comment not closed

- Run-time errors – program directs computer to perform illegal operation. Example:

o dididing by zero

- Undetected errors – program gives incorrect result

- Logic errors – caused by faulty algorithms. Example:

o kms = 1.235*miles;