CSCI 161

Lecture 8

Martin van Bommel

Crafting a Program

• Use comments to tell readers what they need to know, including difficult code

• Use indentation to show bodies of loops

• Use meaningful names

• Use convention for names - lastNumber

• Use standard idioms when appropriate

• Avoid unnecessary complexity

Designing for Change

• #define construct - symbolic constants

#define symbol value

• symbol - name for symbolic constant

• value - replaces symbol in precompilation

• Why? Easier to modify program

Named Constants

• A variable whose content cannot be changed while program is running

const double PI = 3.14159;

• Variable still has data type and memory location, but is read-only

Simple Statements

• Expression followed by semicolon

• Assignments

total = n1 + n2;• Function calls

cout << ”Hello.\n”;• Useless statements

n1 + n2;

Embedded Assignments

• Assignment expression can be used as part of a larger expression in a statement

• Its value is the value assigned

z = (x = 6) + y;• x is assigned value 6, then z assigned 6 + y• Difficult to read• Used rarely and only when makes sense

Multiple Assignments

• Embedded assignments useful to set several variables to the same value

n1 = n2 = n3 = 0;• Assignment operator evaluated right to left

• Avoid mixed types; e.g. double d and int i

d = i = 1.5;• Assigns i value 1, thus 1 assigned to d

Math Library <cmath>Functions for performing math operations

abs(x) absolute value of argument

sqrt(x) square root of argument

pow(y, x) yx

sin(x) sine (argument in radians)

cos(x) cosine (argument in radians)

tan(x) tangent (argument in radians)

log(x) natural logarithm

exp(x) ex