PIC10A Lecture 3

Reading

1.2,1.3,1.4

Input and Output Stream

A stream is a flow of information.

Output Stream

Output Stream is a stream of output generated by the program. e.g. to screen

cout

use cout <<
stands for console output
basically like "print this to screen"
as usual, the statments must end in semicolon (;)

Examples

basic example

cout << "Hello! PIC10A students.";

Here is the output

Hello! PIC10A students.

You can link 2 or more sentences together.

cout << "Hello! " << "PIC10A
students. " << "Welcome to UCLA.";

This is same as

cout << "Hello! ";

cout << "PIC10A students. ";

cout << "Welcome to UCLA. ";

The output is

Hello! PIC10A students. Welcome to UCLA.

You can include variables

int appleNum = 5;

cout << "I ate " << appleNum << " apples this
morning.";

The output is

I ate 5 apples this morning.

appleNum is substituted by its value (5).

You can include arithmetic expressions.

int speed = 45, time = 2;

cout << "I drove " << (speed*time) << " miles.";

Here is the output

I drove 90 miles.

The expression speed*time is evaluated. The value is then printed.
It is better the put parentheses (but not necessary in Visual C++) around the expresion.

Escape Sequences

some characters present difficulties
example, think about the quote marks "
You can cout special characters using "escape sequences"
A backslash, \, preceding a character tells the compiler that the sequence following the backslash does not have the same meaning as the character appearing by itself. Such a sequence is called an escape sequence.

Sequence	Meaning
`\n`	New line
`\t`	tab
`\a`	alert(sounds the alert noise), typically a bell
`\\`	Backslash (allows you to place a backslash in a quoted expression)
`\"`	Double quote(mostly used to place a double quote inside a quoted string)
`\'`	Double quote(mostly used to place a single quote inside single quotes)

Examples

Example

int num1 = 10, num2 = 20;

cout << "The first number is " << num1 

     << ".\nThe second number is " << num2
 << ".\n";

Output

The first number is 10. The second number is 20.

Example

cout << "Backslash \\ is used in
escape sequences.\n";

Output

Backslash \ is used in escape sequences.

Example

cout<<"\"PIC10A is cool,\" Mary
said.\n";

Output

"PIC10A is cool," Mary said.

endl vs "\n"

endl represnets "end line"
It is same as "\n";

cout << "Hello World!\n";

is same as

cout << "Hello World!" << endl;

Formatting for Numbers with a Decimal Point

Example

cout<<"1/11 is "<< 1./11.
<< endl;

Output

1/11 is 0.0909091

Here is the "magic formula". It causes the number to be displayed with the exact number of digits after the decimal point.

#include<iostream>

using namespace std;

      

int main() {

    cout.setf(ios::fixed);

    cout.setf(ios::showpoint);

    cout.precision(2);

   

    cout<<"1/11 is "<< 1./11. << endl;

    return 0;

}

Output

1/11 is 0.09

Exercise: Use cout.precision(3) in the program, what is the output?

Input Stream

Input stream is info fed to the computer for the program.

cin >> variable; or cin >> variable1>> variable2...;
stands for "console input"
Like "read into variables"
when a program reaches a cin statement, it waits for input to be entered from the keyboard.
it sets the first variable equal to the first value typed at the keyboard, the second variable equal to the second value typed....
number in the input must be seperated one or more space or by a line break (return).

Comments

Comments for your program
make your program more readable and easier to modify.
there are 2 types of comment.
you can put comments anywhere in the program.
compilers ignore all the comments. Comments are just for human. It has no effect on programs.
if something is important and not obvious, it merits a comment.

Example

/* PIC
10A Sample Program

      Written by Charles Li

      The program asks the user to
input the number of quarters, dimes, nickels

      and output the total value of
all the coins

*/

#include<iostream>

using namespace std;

      

int main() {

    double quarterValue = 0.25, dimeValue = 0.1,
nickelValue = 0.05;

    int numOfQuarters, numOfDimes, numOfNickels;

    double value; //value
of all the coins

    cout << "Input the number of quarters, dimes
and nickels.\n";

    // ask the user to
input the numbers

    cin >> numOfQuarters >> numOfDimes >>
numOfNickels;

    value = quarterValue*numOfQuarters

           +
dimeValue*numOfDimes 

           +
nickelValue*numOfNickels;

    cout << "The value is " << value
<<".\n";

 

    return 0;

}

Single line comments

// your comment

All the text between the // and the end of the line is a comment

Multi-Lines comments

/* your comment line 1
your comment line2
your comment line 3 */

All the text between /* and */ are comments
line break is allowed

More about types

float and double

floating-point notation, example double x = 3.568902;
scientific notation, example double a = 2.3e-5;(it means 2.3 times 10^-5, or 0.000023)

char

represents a single character (like letters or punctuation marks)
Use single quotes to initalize or assingn : example char ch = 'k';
different from strings. ("Hello world" is a string, "A" is a string, because they are enclosed in double quotes)
can only hold 1 character.

bool

means true or false
example: bool billPaid = false;

Arithmetic Operations and Expressions

C++ allows you to form expresions using variables, and arithmetic operators: +,-,*, /.

Order of operations in expressions

Expressions are evaluated left to right
whatever is in ( ) is first
next is * or /.
finally, + or -

Mixed types

all the arithmetic operators can be used with the number of type int , type double, or one number of each type.
if both numbers are integers, the result is integer
if one of them is double, the result is double

Question
1) What is the type of totalWork in below?

int workDays = 5;

double hours = 7.5;

?????  totalWork
= workDays*hours;

2) What is the return type if a float is added to a double?
3) What is the output of the following program

int a = 7, b = 3;

cout << a/b <<endl;

The % operator

% operator gives the remainder of the division of two integers
e.g. cout << 8%3 << endl; is 2

Shorthand

examples

shorthand	meaning
`a+=1;`	`a = a+1;`
`b-=3.5;`	`b = b-3.5;`
`c*=2;`	`c = c*2;`
`d/=3.1415;`	`d = d/3.1415;`
`e++ ( or ++e)`	`e = e+1;`
`f-- ( or --f)`	`f = f-1;`

Difference between x++ and

++x

Code	`#include<iostream> using namespace std; int main() { int a = 5; int b = a++; cout << b <<endl; return 0; }`	`#include<iostream> using namespace std; int main() { int a = 5; int b = ++a; cout << b <<endl; return 0; }`
Output	5	6
Reason	The code means: `int b = a; a = a+1;`	The code means: `a = a+1; int b = a;`