LECTURE 4:ASSIGNMENTS

PHY 107 – Programming For Science

Announcements

Memorization is not important, but… … you will all still be responsible for

information Instead use your resources: notes, books,

slides, me, ... Via D2L can now get weekly assignment

#2

The Week’s Goal

At end of this week’s lecture, you will be able to

Write (small, useless) C programs

Variable Declarations

Variables must be declared before can be used Way of getting computer to make space for

variable States how to interpret memory in future

uses Allows the compiler to check if uses are

legal

Variables, Constants, & More

General Cases Examples

Variable DeclarationdataType name;dataType name = value;dataType name, anotherName;dataType name = value, anotherName;

int count;bool monkey = true;char help,letter;char a=‘a’,letter;

Constant Declarationconst dataType NAME= value; const double PI=3.1;

Symbolic Constant #define NAME value #define AGE 34

Data Types

Each variable also has data type How program treats variable’s value

defined by this Single true or false value held by bool C/C++ defines 7 numeric data types

Integer types: short, int, long, long long Decimal types: float, double, long double

char data type used to store a character

Variable Names

Begin with letter or underscore (_) Then use any letters, numbers, or

underscore Unique name* needed for each variable

Computer wouldn't know which of 1,000 bobs to use

Reserved words are… reserved and can't be used Reserved words includes void, unsigned, class

Today’s Excitement!

Spent entire day on it, but why create variables? Want to do something with variable

declared C/C++ has large variety of statements to

do this First statement covered in today’s lecture

Assignments

Assignments

Variable declaration creates “box” to store data Box can get values placed in it using

assignments General form of assignment is

variable = expression; Computer works by first evaluating

expression Single value must result from this

expression Once computed, variable’s value is that

result

What Is The Expression?

Simplest expressions are literal values

Examples:double doe;int re;char me;doe = 6;re = 7;doe = -7;doe = 34.5691;me = 'a';me = '0';

12 56 12.345 -56 ‘a’

Data Types

Assignments are legal only if always safe C/C++ defines ordering of legal

assignments

long doubledoublefloatlongintshortchar

Lega

l to

assi

gn to

hig

her

type

What Is The Expression?

Examples of other simple expressionsdouble fa;int so;char la; so = 6;so = 7;fa = -so;so = fa;fa = 34.5691;so = fa;la = 48;so = la;la = so;

What Is The Expression?

Examples of other simple expressionsdouble fa;int so;char la; so = 6;so = 7;fa = -so;so = fa;fa = 34.5691;so = fa; la = 48; so = la;la = so;

What Is The Expression?

Examples of other simple expressionsdouble fa;int so;char la; so = 6;so = 7;fa = -so;so = fa;fa = 34.5691;so = fa;la = 48; so = la;la = so;

What Is The Expression?

Examples of other simple expressionsdouble fa;int so;char la; so = 6;so = 7;fa = -so;so = fa;fa = 34.5691;so = fa;la = 48; // ASCII 48 = '0' so = la;la = so;

What Is The Expression?

Can also include basic arithmetic operators Addition + i = 4 + 6; Subtraction - d = i – 2.3; Multiplication * i = 120 * 8; Division / d = 4.0 / i; Modulus % i = 120 % 8;

Modulus computes remainder between two integers:4 % 5 equals 45 % 4 equals 19 % 3 equals 012823 % 812 equals 643

Tracing A Program

Important for understanding & debugging code Step-by-step execution of program shown To see what is happening, done via pencil-

and-paper Execute each line of program like

computer does Within trace, add row whenever variable

declared Update variable’s value each time it is

assigned Off to side, show output from printf

statements

Program Trace

int main() { int x = 4 + 2; int y = 8 * 1; double z = y – 3; x = x + 1; y = 7 % x; z = y + 1.0 / 2.0; z = 8.0 / 4 + x * x; y = (x – 3) * (y + 2); y = x / 4; return 0;

}

Integer Division

Dividing two integers computes an integer Literals or variables does not matter, only

their type Important to remember, 12 is integer & 12.0 is not

C/C++ ignores result after decimal to get integer2 / 5 equals 0 (the .4 was thrown away) 5 / 2 equals 2 (the .5 was thrown away)16 / 4 equals 4 -5 / 2 equals -2 (the .5 was thrown away)2.0 / 5 equals 0.4 (2.0 is not an integer!)2 / 5.0 equals 0.4 (5.0 is not an integer!)

Floating Point Arithmetic

Operations using decimal has decimal result Even if whole number is result of the

operation For example, all these assignments to i are

illegal:int i;double d = i;i = 6.0 / 3.0;i = 2.0 * d;i = d + 1;i = 4 * 2.0;i = (d * 1) + 5;i = 8 + (9 * 3) – (2 / 1.0) * 4 + 2;

Priority of Operations

Equations can become very complex 4 + 5 * 6 * 9 - 2 + 1 = …?

Very strict order of operations used by computer ( ) Solve from inner- to

outermost + (positive) & - (negative) Solve from right to left * & % & / (division) Solve from left to right + (addition) & - (subtraction) Solve from left to

right

My suggestion: use lots of parentheses

Compound Assignment Operators Short simple operators that allow us to

be lazy Save some typing for several common

actions Lowest priority operation; expression

evaluated first

Operator Equivalent C/C++ Expression

a += 2; a = a + 2;b -= d; b = b – d;c *= 4 + 5.6; c = c * (4 + 5.6);d /= 0.3 * e; d = d / (0.3 * e);

How To Shoot Yourself in Foot Also increment (++) & decrement (--)

operators Use with variables only; no exceptions

possible Used anywhere to save typing an additional

line Two different ways these operators

applied

v = ++b % c; b = b + 1;v = b % c;

c = f * --h; h = h – 1;C = f * h;

a = b++ * c; a = b * c;b = b + 1;

Your Turn

Work on activity in groups until 11:45 Each group will submit 1 copy at end of

class Professor chooses the copy; so must work

together

For Next Lecture

Read pages 69 - 86 for Friday What is this printf thing, anyway? How is it

used? Can we read in input from the keyboard?

How?

Week #2 weekly assignment already posted Next assignment will be due on Tuesday at

5PM Problem #1 not from today; only time this

happens