Assignment 1 due Thursday 12:00 midnight

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Project 1 assigned tomorrow:

Hint:  Practive writing simple programs, output and mathematic operations.

Variable Types (re-visited)

What is a variable?

• Something that Varies.
• A non-constant value that may be assigned different values throughout execution of the program.

Variable Types (re-visited)

How is a variable represented in the computer?

• Binary Code ( a base 2 number)
• 4 = 0100, 7 = 0111, etc...

Variable Types (re-visited)

What is so important about variables anyway?

• They are temporary storage

Running Programs

• What is a program?
• Compiling
• Linking
• Executing

Running Programs

What is a program?
• An executable string of binary numbers that menas something to a computer, i.e. tells the computer how to perform a certain operation
• We allow ourselves to get away from this, and write programs in a high-level language such as C++

Running Programs

Compiling
• This turns the high-level language information, such as:

 

 
 
 

x = 3*4+5;
 

• into something that the com0puter can understand:

 

 
 
 

mov 3, r1
mul r3, 4, r1
add r3, 5, r3
st  r3, [@x]
 

• or, even worse, what hte computer really understands:

 

 
 
 

11110000010100100000001100000001
01101000010101100000010000000001
10101000010101100000011100000011
11111111010101100000000000011011
 

Compiling
• What we do to compile:
• % g++ -o program program.C

Running Programs

Linking
• This is done automatically by the compiler
• Sets everything up so that the program will run

Running Programs

Execution
• Actually running the program
• Type the program name
• a.out, program, whatever...
• Loads the program into the computer's memory and executes the instructions found therein.

Programming

Art or Science?
Both?

Programming

Algorithms
Design

Programming

Algorithm:
• A deterministic set of instructions which ALWAYS produces the answer derived from those instructions.
• A set of instructions for performing a certain task:

turn left from the front door
walk straight for four street blocks
turn left
walk straight until you get to the store
walk straight into the store until you get to the freezers
get three TV Dinners
turn around
walk straight to one of the checkstands
when the cashier asks you for money
pay for the meals
return home

Programming

Design
• Just like anything, you have to plan how you are going to attack the problem for which you are creating a program.

Programming

Design
• Just like anything, you have to plan how you are going to attack the problem for which you are creating a program.

C++ History

• Kernigan and Ritchie
• AT&T Bell Labs
• B
• C
• C++
• Why?

C++

Simple program:

<one or more includes>
using namespace std;

int main() {
<one or more statements>
  return 0;
}
 

C++

Simple program (filled out):

#include <iostream>
using namespace std;

int main() {
  cout << "Good morning, Dave." << endl;
  return 0;
}
 

C++

Simple program (filled out):

#include <iostream>
using namespace std;

• #include <iostream>  is necessary for the use of the cout variable, and the << operator.
• using namespace std; is necessary to access the definitions inside the included iostream.

C++

Simple program (filled out):

int main() {

• int main()  is the first, and only function that you will use now.
• Operating System calls main() to execute your program, when you execute your program from the command line.
• { is there to start the function definition of main, this tells the compiler that you are starting a block, and to, whenever main is called, execute everything between this ({) and the ending brace, (})

C++

Simple program (filled out):

cout << "Good morning, Dave." << endl;

• cout says that you want to send the output to the standard output, for now this is the only one that you will use
• << says that you want to 'put' something in cout
• "Good morning, Dave." is what you want to put into cout
• <<   --  you want to put something else in cout.
• endl  -- put and endline into cout

C++

Simple program (filled out):

  return 0;
}

• return 0; says that you want to end the program, and if anyone is watching, then it should send 0 back to them.
• } ends the function main.

C++

reading a program:
 

• cout << "Good morning, Dave." << endl;
• put, into cout, the string (") Good morning, Dave (") and then put an endline into cout as well.
• Why not:  cout << "Good morning, Dave." endl;
• Because, "Good morning, Dave" is one thing and endl is another, therefore since you can only 'put' one thing into cout at a time, it causes an error.