Arithmetic Expressions

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

- arithmetic expression consists of operators and operands

- arithmetic operators: +, -, *, /, % (remainder, used only with int type)

- operands can be constants, variables, or other arithmetic expressions

- examples of arithmetic expressions:

3 + 6

6 - 7 * 2

x + 3 * y

- result of arithmetic expression is often stored in a variable of int or double type through an assignment statement:

x = 3 * y;

Division Operator (x / y)

- there is an important difference whether operands are int or double types

o for int type, / computes the integral part of the division

7 / 2 equals 3, not 3.5

o for double type, / represents the standard division

7.0 / 2.0 equals 3.5

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

Remainder Operator (x % y)

- only applicable on int types

- produces remainder of a division

o 7 % 2 equals 1

o 23 / 6 equals 5

- useful equation for int variables m and n:

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

Data Type of an Expression

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

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

- expressions that have operands of both type int and double are allowed and are called mixed-type expressions

Mixed-Type Assignment Statements

- how assignment works with mixed-type expressions:

o expression on right is evaluated 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

e.g.       int k, m, n;

              double p, x ;

m = 3;

              n = 2 * 1.2;

              p = 2;

              x = m / n;

              x = m / p;

              k = m / n;

              k = x / p;

Type Conversion Using 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;   /* y will be 2.5 */

y = (double) m / n;   /* y will be 2 since division has precedence over type cast */

Unary Operators

- + and - can be unary or binary operators

o x = -y;   /* unary */

o z = y - x;     /* binary */

Rules for Evaluating Complex Expressions:

- Parenthesis rule (executed from the inside out)

- Operator precedence:

o unary +, -

o *, /, %

o binary +, -

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

o x * y * z + a / b – c * d EQUALS (x*y*z) + (a/b) – (c*d)

Writing mathematical formulas in C

- look at examples from Table 2.10 in the textbook

Formatting Numbers in Program Output

- printf provides capability to print neat outputs to the screen

- it can be achieved by adding numbers after placeholdes,

o %5d means that at least 5 spaces will be taken to display an integer value

o %6.2f means that two digits are reserved for the fractional part, and at least 6 total spaces will be used to print a real-vallued variable

- read section 2.6 from the textbook

- pay attention to Tables 2.11, 2.12, 2.13

Common Programing Errors

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

o missing semicolon

o undeclared variable

o comment not closed

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

o dividing by zero

- Undetected errors – program gives incorrect result

- Logic errors – caused by faulty algorithms. Example:

o kms = 1.235*miles;