Fundamentals of Programming Lecture 2: Input and Output, Lecture notes of Programming for Engineers

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Fundamentals of

Programming

Lecture

Input and Output

• (^) A data stream is a sequence of data
  • (^) Typically in the form of characters or numbers
• An input stream is data for the program to use - (^) Typically originates - (^) at the keyboard
• (^) at a file
• An output stream is the program’s output - (^) Destination is typically - (^) the monitor
• (^) a file

Examples Using cout

• (^) This produces the same result as the previous sample cout << number_of_bars ; cout << " candy bars\n";
• (^) Here arithmetic is performed in the cout statement cout << "Total cost is $" << (price + tax);
• (^) Quoted strings are enclosed in double quotes ("Walter") - Don’t use two single quotes (')
• (^) A blank space can also be inserted with cout << " " ;

Include Directives

• (^) Include Directives add library files to our programs
  • (^) To make the definitions of the cin and cout available to the program: #include
• (^) Using Directives include a collection of defined names
  • (^) To make the names cin and cout available to our program: using namespace std;

Reading Data From cin

• (^) Multiple data items are separated by spaces
• (^) Data is not read until the enter key is pressed
  • (^) Allows user to make corrections
• (^) Example: cin >> v1 >> v2 >> v3;
• Requires three space separated values
  • (^) User might type 34 45 12

Designing Input and Output

Prompt the user for input that is desired

• (^) cout statements provide instructions

cout << "Enter your age: ";

cin >> age;

• Notice the absence of a new line before using cin

Echo the input by displaying

what was read

• (^) Gives the user a chance to verify

data

Very Simplistic View of a Computer CPU Location 0 Location 1 Location 2 Location 3 Location 4 Location 5 Each location is 1 byte of memory 1 byte = 8 bits Each bit is an electric impulse carrying 1 or 0. This simplistic view is enough to explain the basic concepts of programming to students 5

Valu

e

• (^) The only task a computer can do is arithmetic e.g. multiplying, dividing, subtracting, etc.
• (^) Therefore, everything in the computer is represented as a value
• Numbers, letters, characters, etc are all represented as values
• (^) Values could change depending on their nature. For example
• the temperature today is different from the temperature yesterday
• The number of cars inside Lahore is different then the number of in cars Islamabad.

Variable

To store a value inside a computer a

‘variable’ is used.

A variable is a space in the memory to

store a value.

This space is reserved until the variable

is required.

Session 2 7

What Makes a Variable

Variable has three important characteristics:

• (^) Type
  • (^) How much memory do a variable need.
    • This information is determined by a type.
• (^) Name
• (^) How to differentiate a variable with another variable of the same type.
• Name refers to the memory location assigned to this variable.
• (^) Value
  • (^) What is the value?
    • The actual value contained by a variable. Session 2 8

Example of a Variable (Memory View) int temperature = 35 Locations 0 - 3 are collectively called as ‘temperature’ 00000000 00000000 00000000 00100011 100011 is the binary equivalent of 35 Location 0 Location 1 Location 2 Location 3 Location 4 Location 5 Session 2 10

Changing the Value of Variable

Session 2

Lets change the value of

‘temperature’.

temperature = 45902 1011001101001110 is the binary equivalent of 45902 00000000 Location 0 Locations 0 - 3 are collectively (^00000000) Location 1 called as ‘temperature’ 10110011 Location^2 (^01001110) Location 3 Location 4 Location 5 11

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 double mpg; mpg = 26.3; // declare the variable // initialize the variable
• (^) Declaration and initialization can be combined using two methods
• (^) Method 1 double mpg = 26.3, area = 0.0 , volume;
• (^) Method 2 double mpg(26.3), area(0.0), volume;

Variable for Real Numbers

int cannot hold a real value.

Therefore, a type “double” is used to hold real

values.

Double takes 8 bytes of memory instead of 4 bytes

of a double.

Out of the 8 bytes in a double 4 bytes are used to

hold the value before the decimal point and 4

bytes for the value after the decimal point.

ession 2 14