C++ Programming Basics Chapter 1 Lecture CSIS 10A

C++ Programming Basics

Agenda

Hardware Basics  The IDE

My First Program

Its all G(r)eek to me

Anatomy of a Computer

Memory Output

ALU Control Input

The CPU uses machine language

Compilers to the Rescue!

High level languages like C++ allows writing code that is easier to understand and

universally works on any CPU. circle=2.0*radius*pi;

Agenda

Hardware Basics The IDE 

My First Program

Its all G(r)eek to me

THE MECHANICS OF WRITING

A PROGRAM

1. Editing -- Writing a program

2. Compiling -- Translating from C++ into machine language 3. Linking -- Combining your program with other libraries 4. Running – Letting the computer execute a program

5. Debugging – Running step by step through a program searching for mistakes

Agenda

Hardware Basics The IDE

My First Program  Its all G(r)eek to me

Hello World !

Lets start off the traditional way

Program that prints out “Hello World” on your output console (your screen)

Steps

1. Create new source file 2. Write the code

3. Create a workspace (only in MSVC++) 4. Compile

5. Link

Agenda

Hardware Basics The IDE

My First Program

Its all G(r)eek to me 

It’s all G(r)eek to me

… actually, its C++

20,000 ft. above sea level

#include <iostream> using namespace std; int main()

{

// This is my first program

cout << "Hello World" << endl; system("pause");

20,000 leagues under the sea

#include <iostream>

Actually includes some information into your code

Contains some definitions that are needed for your code

22,000 leagues under the sea

using namespace std;

This line refers to a set of standard object name definitions

… deeper….

int main()

• This is the piece of code (function) that is operated on first when a program is executed

• What’s a function ???

… even deeper….

//This is my first program

• This is a comment you write to yourself • Useful when writing large programs

… and deeper…..

Output operator

cout << “Hi”<<endl;

cout is the console monitor (your display)

<< is the output operator. Use to chain together your output message.

“Hi”is a string literal

… getting sleepy?…..

For the Bloodshed environment…Hold the display open so you can read it

(pressing a key will continue)

system("pause");

Finish up this program, return a 0 to operating system (everything ended OK)

… and even deeper ….

{} delineates the code block

Other types of cout statement

cout<< “ my age is” <<endl << 39<<endl; cout<< “ my age is 39”;

cout<< “ what’s your’s”; Escape with \

Tom’s All Purpose Program Shell

#include <iostream> using namespace std; int main()

{

// Your code here ...

system("pause"); return 0;

}

You Do It

Modify your hello world program to print your name, address and phone number (COULD BE FAKE!) on three lines:

Tom Rebold

1600 Pennsylvania Ave 123-456-7890

Lets get moving…..

We’ll learn as we proceed

You’ll be saying “Aha!” or “Oho!” when you hear these terms again

What more ?

Variables and Declarations

Variables represent storage locations in the computer’s memory

variable = expression

Assignment is from right to left

n = 5;

Using int Variables

Clearing the haze

int m;

m

int

Want more ?

User Input with

cin

How shall I feed in data ?

Remember cout ?

Meet cin

cin >> m;

User Input with

cin

int main() {

cout << "Enter the value of m:"; cin >> m;

User Input with

cin

int main() {

User Input with

cin

int main() {

int m;

cout << "Enter the value of m:"; cin >> m;

Your turn ()

1. from hello.cpp File>SaveAs age.cpp

2. Delete all the cout statements. Add lines to: a) Declare a variable called age

b) Display a message asking for data (such as “tell me your age”)

c) read the data into age

That’s a wrap !

What we learned so far:

How to write a basic C++ program The structure of a program

Displaying to the console (cout) Variables

C++ Programming Basics

Agenda

Review 

An Intermediate Program

Making a Program Interactive Assignment Statements

Standard Program Structure File output

Review –Identify each piece

#include <iostream> using namespace std; int main()

{

// this program stores data in a variable

int m;

cout << “Enter the value of m:”; cin >> m;

cout << “m = “ << m << endl; system(“pause”);

Variables and Assignments

Variables are like small blackboards

We can write a number on them We can change the number

We can erase the number

C++ variables are names for memory locations

We can write a value in them

Review –what does this show?

int x;

x=6;

x=8;

Identifiers

Variable names are called identifiers Choosing variable names

Use meaningful names that represent data to be stored

First character must be

• a letter

• the underscore character _

Remaining characters must be

• letters • Numbers

Which identifiers are legal?

feet Average score

1993tax Average_score

Sum Average.score

Keywords

Keywords (also called reserved words)

Are used by the C++ language

Must be used as they are defined in the programming language

Cannot be used as identifiers Examples (75 altogether):

Declaring Variables

Before use, variables must be declared

Tells the compiler the type of data to store Examples: int one_weight, total_weight;

int represents whole numbers • Could store 1, 4, -345, etc.

Declaring Variables

int main() {

 int score1, score2, sum;

cin>> … etc … sum=score1+score2;

… etc …

Declaring Variables

Declaration syntax:

Type_name Variable_1 , Variable_2, . . . ;

Declaration Examples:

int m_score, total_score; float moon_distance;

int age, num_students; char grade;

Agenda

Review

An Intermediate Program  Making a Program Interactive Arithmetic

An intermediate C++ program:

// height.cpp

// Convert height in feet to inches. #include <iostream>

using namespace std; int main()

{

int feet, inches; feet = 6;

inches = feet * 12;

cout << "Height is " << inches << " in."; return 0;

Execution – what you see

Execution – what really happens

int feet, inches;

Execution – what really happens

cout << "Height is " << inches << " in.";

feet

int

72 inches

Agenda

Review

An Intermediate Program

Making a Program Interactive  Arithmetic

Interactive Program

The previous program always runs exactly the same way (Height is 72 in)

We’d like to be able to “put in” the data we want to process

So we add two more lines. One asking for data:

cout<<“What is height in feet?”<<endl;

The other takes input:

An intermediate C++ program:

// height.cpp

// Convert height in feet to inches. #include <iostream>

using namespace std; int main()

{

int feet, inches;

cout << “What is height in feet?” << endl; //******** cin >> feet; //********

inches = feet * 12; cout << "Height is " << inches << " in."; return 0;

Basic Interactive Program

int main() {

1) Declare Variables

2) Ask (prompt) for data 3) Input data

4) Calculate result

A clever use of comments

Inside Lab1Basics.cpp are 10 programming problems…how to keep separate?

Remember // ignore to end of line

Another type of comment works in “blocks” :

/* start a block comment ignored

Combine the two…

/**** Problem 1 ********

// Here are your instructions

(space for your code)

Agenda

Review

An Intermediate Program

Making a Program Interactive Arithmetic 

Assignment Statements

An assignment statement changes the value of a variable

total_weight = one_weight + number_of_bars;

• total_weight is set to the sum one_weight + number_of_bars

Assignment statements end with a semi-colon

The single variable to be changed is always on the left of the assignment operator ‘=‘

On the right of the assignment operator can be

• Constants -- age = 21;

Assignment Statements and Algebra

The ‘=‘ operator in C++ is not an equal sign

The following statement cannot be true in algebra

number_of_bars = number_of_bars + 3;

Initializing Variables

Declaring a variable does not give it a value

Giving a variable its first value is initializing the variable

Variables are initialized in assignment statements int miles, area; // declare the variables

miles = 26; // initialize the variable area=0; // initialize

Declaration and initialization can be combined int miles = 26, area = 0.0;

Arithmetic in C++

Basic operations + - * /

A = pr2 area=radius*radius*3.14; F = (v -a) force=(v-a)/(v+a);

(v+a)

Can you guess what is stored in x?

int a, b=3, c, x; a=b*2;

c=a+3; x=c-2;

Program flow is sequential (top to bottom)

a b c x

? 3 ? ?

6 3 ? ?

6 3 9 ?

Your turn…what is stored in x?

int a, b, c, x=3; a=2;

x=3+a; x=x+a;

Program flow is sequential, order matters!!

Agenda

Review

An Intermediate Program Arithmetic

Standard Program Structure

To solve most problems, your main() program will generally look like this (conceptually) 1. Declare variables for input, result and

intermediate data 2. Ask for data

3. Input data (cin) 4. Calculate result

Another interactive C++ program:

// Convert input number of nickels and dimes // to cents.

#include <iostream> using namespace std; int main()

{

int nickels, dimes, cents;

cout << "Enter number of nickels and dimes: "; cin >> nickels >> dimes;

cents = 5 * nickels + 10 * dimes; cout << nickels << " nickels and "

<< dimes << " dimes " << "= " << cents << " cents " << endl; return 0;

Your Turn

Run the previous code, found in Lab1Basics problem4, and verify it works correctly

Agenda

Review

An Intermediate Program Arithmetic

Syntax Errors

cout << "Hello" << endl; N = 2;

cout << "n eqalls " << n cout << "So long << endl; system("pause");

return 0;

This program has 3 errors

Tracking them down

Syntax—

double click on the first error message it takes you to that line of code

Look at or above that line for possible errors Fix it and try again

Errors often create other errors

That’s a wrap !

What we learned today:

How to write an intermediate C++ program Standard program structure

Go back home proud !