Computer Science 1620 Selection Structures. Write a program that accepts the speed of a vehicle, and determines whether that person is speeding assume

Computer Science 1620

Selection Structures

Write a program that accepts the speed of a vehicle, and determines whether that person is speedingassume speed limit = 100 km/h

Suppose that I invest $25000 into a mutual fund that returns 8% per year. Write a program to calculate how much the fund will be worth after a) ten years, b) twenty years c) thirty years

Write a program that accepts the speed of a vehicle, and determines whether that person is speeding.

#include <iostream> using namespace std;

int main() {

const int LIMIT = 100;

int num; cout << "Speed: "; cin >> num;

cout << boolalpha; cout << "Car is speeding: " << ( speed > LIMIT ) << endl;

return 0;

}




int main() {


int num; cout << "Speed: "; cin >> num;


return 0;

}




int main() {


int speed; cout << "Speed: "; cin >> speed;


return 0;

}




int main() {




return 0;

}




int main() {




return 0;

}

The previous program worksLimitations:

the program tells us whether the expression is true or false

what if we wanted to perform some statement only when a person is speeding:

output "Car is speeding" calculate the speeding ticket etc

Selection Structuresallow the conditional execution of certain

statementsmay or may not be executed

two types: if-else statementsswitch statements

If Statementsyntax:

if ( )

C++ Statement

boolean expression

this statement will be executed IF AND ONLY IF this expression has value true

Example: from the previous program, output "Car is

speeding!" if the car is exceeding the speed limit




int main() {




return 0;

}




int main() {



return 0;

}

if ( )

C++ Statement

boolean expression




int main() {



return 0;

}

if ( )

cout << "Car is speeding!" << endl;

boolean expression




int main() {



return 0;

}

if ( )

cout << "Car is speeding!" << endl;

speed > LIMIT




int main() {



if (speed > LIMIT) cout << "Car is speeding!" << endl;

return 0;

}

What statements are legal in an if statement?

if ( )

C++ Statement

boolean expression

Answer: almost anything• I/O statements (cin, cout)• variable declarations, assignments• expressions• etc

One if – many statementssuppose the cost of a speeding ticket is

$100 plus an additional $2 for each km over the speed limit

adapt our program so that if a car is speeding, it prints "Car is speeding", and prints the price of the speeding ticket in a different statement




int main() {




return 0;

}



#include <iostream>#include <iomanip> using namespace std;

int main() {



cout << setprecision(2) << fixed << showpoint;

if (speed > LIMIT) cout << "Car is speeding!" << endl; cout << "Ticket: $" << 100.00 + 2 * (speed – LIMIT) << endl;

return 0;

}

One if – many statementswhen an if statement is used, only the

subsequent statement is affected in our example, the speeding ticket

calculation was not part of the if statementso it is always executed

how do we fix this?Solution 1: use two if statements




int main() {




if (speed > LIMIT) cout << "Car is speeding!" << endl; cout << "Ticket: $" << 100.00 + 2 * (speed – LIMIT) << endl;

return 0;

}




int main() {





if (speed > LIMIT) cout << "Ticket: $" << 100.00 + 2 * (speed – LIMIT) << endl;

return 0;}

One if – many statements the previous solution worksProblem:

inefficient: repeated codeslow: what happens If we have 20 different

statements to be conditionally executed

Compound Statementssyntax:

{

}

statement 1;

statement 2;

statement 3;

statement n;

…

• Each statement is a C++ programming statement

• Executed normally

• When used with a control structure, it is treated as a single C++ statement




int main() {





if (speed > LIMIT) cout << "Ticket: $" << 100.00 + 2 * (speed – LIMIT) << endl;

return 0;}




int main() {




if (speed > LIMIT) { cout << "Car is speeding!" << endl; cout << "Ticket: $" << 100.00 + 2 * (speed – LIMIT) << endl; }

return 0;

}




int main() {





return 0;

}

The entire compound statement is associatedwith the if statement.

Elseconsider the program output when a car is

not speeding:

• Nothing to indicate that any computation is taking place

ElseSolution: When someone is not speeding,

output: "Car is not speeding!"




int main() {





return 0;

}




int main() {





if (speed <= LIMIT) cout << "Car is not speeding!" << endl;

return 0;

}

Else the previous solution worksProblem:

inefficient: repeated test

Solution: else

ElseSyntax:

if ( )

else

C++ Statement

boolean expression

C++ Statement

if expression is true, this statement is executed

if expression is false, this statement is executed




int main() {





if (speed <= LIMIT) cout << "Car is not speeding!" << endl;

return 0;

}




int main() {




if (speed > LIMIT) { cout << "Car is speeding!" << endl; cout << "Ticket: $" << 100.00 + 2 * (speed – LIMIT) << endl; } else cout << "Car is not speeding!" << endl;

return 0;

}

A quick note about if … else some programmers will use braces with their if

statements, even if there is only one statement

Programmer preference – and will be treated as such on your assignments/exams

if (speed > LIMIT) { cout << "Car is speeding!" << endl;} else { cout << "Car is not speeding!" << endl;}

Example: Suppose there are two scholarships available to

university students. Scholarship A requires that the student is from Alberta, while scholarship B requires that the student is from Alberta AND has a GPA of 80%. Write a program that reads whether a person is from Alberta, and their GPA, and determines their eligibility for each scholarship.


Write a program that reads whether a person is from Alberta, and their GPA, and determines their eligibility for each scholarship.


int main() {

bool albertan; float gpa;

cout << "Are you from Alberta (0=no, 1=yes): "; cin >> albertan;

cout << "GPA: "; cin >> gpa;

if (albertan) cout << "You are eligible for scholarship A." << endl;

if (albertan && gpa >= 80.0f) cout << "You are eligible for scholarship B." << endl; return 0;

}




int main() {






}




int main() {






}




int main() {






}




int main() {






}

Scholarship A requires that the student is from Alberta




int main() {






}

Scholarship A requires that the student is from Alberta




int main() {






}

Scholarship B requires that the student is from Alberta and has a GPA of 80 or better.




int main() {






}

Scholarship B requires that the student is from Alberta and has a GPA of 80 or better.

The following program works, but there is an inefficiency

How do we fix this? recall that almost any C++ statement can be included in an if statement the if statement itself is a C++ statement therefore, we can nest one if statement inside the other.


if (albertan && gpa >= 80.0f) cout << "You are eligible for scholarship B." << endl;

• We test for albertan being true twice.




int main() {






}




int main() {




if (albertan) { cout << "You are eligible for scholarship A." << endl; if (albertan && gpa >= 80.0f) cout << "You are eligible for scholarship B." << endl; }

return 0;

}




int main() {




if (albertan) { cout << "You are eligible for scholarship A." << endl; if (gpa >= 80.0f) cout << "You are eligible for scholarship B." << endl; }

return 0;

}

Nested If Statementswhen an if statement is used within another

if statement, the second if statement is called nested

we can nest as many if statements as we like

example: Scholarship C requires a student to be from Alberta, have a GPA of 80%, and be a full time student. Incorporate this scholarship information into the previous program.




int main() {





return 0;

}




int main() {

bool albertan; float gpa; bool fulltime;



cout << "Full time or part time (0=part, 1=full): "; cin >> fulltime;


return 0;

}




int main() {

bool albertan; float gpa; bool fulltime;



cout << "Full time or part time (0=part, 1=full): "; cin >> fulltime;

if (albertan) { cout << "You are eligible for scholarship A." << endl; if (gpa >= 80.0f) { cout << "You are eligible for scholarship B." << endl; if (fulltime) cout << "You are eligible for scholarship C." << endl; } } return 0;}

Nested If Statement the else clause can be embedded into an if statement as well

Example: Suppose you know that a person is either from Alberta or Saskatchewan. Write a program that reads whether the person is from Alberta, and whether the person lives in the north or south half of the province. The program then outputs the area code of that person's phone number.

North South

Alberta 780 403

Saskatchewan 306 306


Write a program that reads whether the person is from Alberta, and whether the person lives in the north or south half of the province. The program then outputs the area code of that person's phone number.


int main() {

bool albertan; bool north;

cout << "Which province are you from (0=Saskatchewan, 1=Alberta): "; cin >> albertan;

cout << "Where in your province are you from (0=south, 1=north): "; cin >> north;

if (albertan) if (north) cout << "Your area code is 780" << endl; else cout << "Your area code is 403" << endl; else cout << "Your area code is 306" << endl;

return 0;}


Write a program that reads whether the person is from Alberta, and whether the person lives in the north or south half of the province. The program then outputs the area code of that person's phone number.#include <iostream> using namespace std;

int main() {





return 0;}



int main() {





return 0;}



int main() {





return 0;}



int main() {





return 0;}

North South

Alberta 780 403




int main() {





return 0;}

North South

Alberta 780 403




int main() {





return 0;}

North South

Alberta 780 403




int main() {





return 0;}

North South

Alberta 780 403




int main() {





return 0;}

North South

Alberta 780 403




int main() {





return 0;}

North South

Alberta 780 403




int main() {





return 0;}

North South

Alberta 780 403




int main() {





return 0;}

North South

Alberta 780 403


Nested Ifnested ifs and elses must be used

cautiously

Example: Suppose you didn't know the area code for southern Alberta.

hence, you choose to omit outputting this from your program

NOTE: 780 still only applies to northern residents



int main() {





return 0;}

North South

Alberta 780 ????




int main() {





return 0;}

North South

Alberta 780 ????




int main() {




if (albertan) if (north) cout << "Your area code is 780" << endl; else cout << "Your area code is 306" << endl;

return 0;

}

North South

Alberta 780 ????




int main() {





return 0;

}

North South

Alberta 780 ????




int main() {





return 0;

}

North South

Alberta 780 ????


else matches to closest if

Nested ifsan else statement will always match to its

closest visible if statementan else statement that is outside a

compound statement (block) cannot see into that compound statement (block)



int main() {





return 0;

}

North South

Alberta 780 ????




int main() {




if (albertan) { if (north) cout << "Your area code is 780" << endl; } else cout << "Your area code is 306" << endl;

return 0;

}

North South

Alberta 780 ????


Why did this work?

since second if statement is inside block and else statement is outside of that block, else cannot see the inside if

therefore, closest visible if is the first if we will examine scope more closely later on



Example: Consider again the amusement park ride. Rewrite the program so that anyone under 32" is told that they are too short, while anyone above 60" is told they are too tall.


Write a program that reads a height (in inches), and computes whether that person is eligible.


int main() {

int height; cout << "Please enter your height: "; cin >> height;

cout << boolalpha;

cout << "This person is eligible to ride: " << ((height >= 32) && (height <= 60)) << endl;

return 0;

}Rewrite using an if statement.




int main() {


if ((height >= 32) && (height <= 60)) cout << "You are eligible to ride. " << endl; else cout << "You are not eligible to ride. " << endl;

return 0;

}Rewrite using an if statement.




int main() {


if ((height >= 32) && (height <= 60)) cout << "You are eligible to ride. " << endl; else cout << "You are not eligible to ride. " << endl;

return 0;

}Rewrite, specifying whether a person is too tall, or too short.




int main() {


if (height >= 32) if (height <= 60) cout << "You are eligible to ride. " << endl; else cout << "You are too tall to ride. " << endl; else cout << "You are too short to ride. " << endl;

return 0;

}

Rewrite, specifying whether a person is too tall, or too short.

Else if when a decision has more than two outcomes (as in the

previous example), it is often written using an else if format Syntax:

if ( )

else if ( )

else if ( )

else

C++ Statement

boolean expression 1

executed if expression 1 is true


C++ Statement

C++ Statement


C++ Statement



executed if none of the expressions are true




int main() {


if (height >= 32) if (height <= 60) cout << "You are eligible to ride. " << endl; else cout << "You are too tall to ride. " << endl; else cout << "You are too short to ride. " << endl;

return 0;

}

Rewrite with an else if format.



#include <iostream>

using namespace std;

int main() {

int height;

cout << "Please enter your height: ";

cin >> height;

if (height < 32)

cout << "You are too short to ride. " << endl;

else if (height > 60)

cout << "You are too tall to ride. " << endl;

else if ( (height >= 32) && (height <= 60))

cout << "You are eligible to ride. " << endl;

return 0;

}



#include <iostream>


int main() {

int height;


cin >> height;

if (height < 32)




else if ( (height >= 32) && (height <= 60))


return 0;

}

Do we really need to test this?



#include <iostream>


int main() {

int height;


cin >> height;

if (height < 32)




else


return 0;

}

Else if – Advantageseasier to read and write

no need to parse complicated nested if expression

no worries about incorrect if/else matching

Else if – How it works else-if is not something special in the language

the second if is just the statement for the first else the third if is just the statement for the second else etc …

if (height < 32)




else


if ( )

else

C++ Statement

boolean expression

C++ Statement

Example:

Example:The monthly income of a computer

salesperson is calculated by the following commission schedule:

Monthly Sales Income

Greater than $50K $375 + 16% of sales

Less than $50K but greater than or equal to $40K $350 + 14% of sales




Less than $10K $200 + 3% of sales

*From Program Development and Design Using C++, by Gary Bronson

Write a C++ program that calculates and outputs the monthly income of a computer salesperson based on sales.


int main() {

double monthlySales, income;

cout << "Enter the value of monthly sales: "; cin >> monthlySales;

if (monthlySales >= 50000.00) income = 375.00 + 0.16 * monthlySales;

if ((monthlySales < 50000.00) && (monthlySales >= 40000.00)) income = 350.00 + 0.14 * monthlySales;




if (monthlySales < 10000.00) income = 200.00 + 0.03 * monthlySales;

cout << fixed << showpoint << setprecision(2) << endl; cout << "The income is $" << income << endl;

return 0;}



int main() {










return 0;}



int main() {










return 0;}










int main() {










return 0;}










int main() {










return 0;}










int main() {










return 0;}










int main() {










return 0;}



int main() {










return 0;}



int main() {










return 0;}

How many comparisonsare made if monthlySalesis $75000?



int main() {




else if ((monthlySales < 50000.00) && (monthlySales >= 40000.00)) income = 350.00 + 0.14 * monthlySales;




else if (monthlySales < 10000.00) income = 200.00 + 0.03 * monthlySales;


return 0;}

How many comparisonsare made if monthlySalesis $75000?



int main() {








else if (monthlySales < 10000.00) income = 200.00 + 0.03 * monthlySales;


return 0;}

Redundant comparisons!



int main() {




else if (monthlySales >= 40000.00) income = 350.00 + 0.14 * monthlySales;




else income = 200.00 + 0.03 * monthlySales;


return 0;}

Example:

Write a program that takes in an integer, an char, and an integer. If the char is a '+', then print the addition of the two integers. If the char is a '-', then print the subtraction of the two integers. If the char is a '*', then print the multiplication of the two integers. If the char is a '/', then print the division of the two integers. If the char is a '%', then print the modulus of the two integers. If the char is none of these, then print "Unknown operation!"


int main() {

int left, right; char op;

cout << "Please enter your equation: "; cin >> left >> op >> right;

cout << left << " " << op << " " << right << " = ";

if (op == '+') cout << (left + right) << endl;

else if (op == '-') cout << (left - right) << endl;

else if (op == '*') cout << (left * right) << endl;

else if (op == '/') cout << (left / right) << endl;

else if (op == '%') cout << (left % right) << endl;

else cout << "Unknown operation" << endl;

return 0;}



int main() {










return 0;}



int main() {










return 0;}



int main() {










return 0;}



int main() {










return 0;}



int main() {










return 0;}



int main() {










return 0;}



int main() {










return 0;}


Switch an alternative to an if … else chain syntax:

switch ( ) {

integer literal

integer expression

case :

C++ statements

break;

integer literalcase :

C++ statements

break;default:

C++ statements

}

Switch – How it works

switch ( ) {

integer literal

integer expression

case :

C++ statements

break;


C++ statements

break;default:

C++ statements

}


switch ( ) {

integer literal

integer expression

case :

C++ statements

break;


C++ statements

break;default:

C++ statements

}

Step 1: Expression is evaluated.


switch ( ) {

integer literal

integer expression

case :

C++ statements

break;


C++ statements

break;default:

C++ statements

}

Step 2: Program attempts to find a literal in a case statement that matches the value of the expression.


switch ( ) {

integer literal

integer expression

case :

C++ statements

break;


C++ statements

break;default:

C++ statements

}

Step 2a: If program finds a match between expression and literal, then it executes all statements following that case statement until it hits a break statement.


switch ( ) {

integer literal

integer expression

case :

C++ statements

break;


C++ statements

break;default:

C++ statements

}

Step 2b: If program finds no match between expression and literal, then it executes all statements following the default statement

Example: Write a program that reads an integer from the user. If the integer is a 1, then print the string "One". If the integer is a 2, then print the string "Two". If the integer is a 3, then print the string "Three". Otherwise, print "I can only count to three".


int main() {

int num;

cout << "Please enter a number: "; cin >> num;

switch (num) { case 1: cout << "One" << endl; break; case 2: cout << "Two" << endl; break; case 3: cout << "Three" << endl; break; default: cout << "I can only count to three." << endl; } return 0;}

Write a program that reads an integer from the user. If the integer is a 1, then print the string "One". If the integer is a 2, then print the string "Two". If the integer is a 3, then print the string "Three". Otherwise, print "I can only count to three".


int main() {

int num;





int main() {

int num;





int main() {

int num;





int main() {

int num;





int main() {

int num;





int main() {

int num;




Switch Statement the default in a switch is optional

like the else in an if statement if no default code is given, then no computation

is done in the event of no matching value


int main() {

int num;



Write a program that reads an integer from the user. If the integer is a 1, then print the string "One". If the integer is a 2, then print the string "Two". If the integer is a 3, then print the string "Three". Otherwise, do nothing.


int main() {

int num;


switch (num) { case 1: cout << "One" << endl; break; case 2: cout << "Two" << endl; break; case 3: cout << "Three" << endl; break; }

return 0;}

Write a program that reads an integer from the user. If the integer is a 1, then print the string "One". If the integer is a 2, then print the string "Two". If the integer is a 3, then print the string "Three". Otherwise, do nothing.

Switch Statement the expression and literals must be an integer type

booleans char short int long

each case statement contains only a single literal cannot indicate a range of statements

Switch Statement if an if-else chain:

1) has expressions that all use == AND2) is comparing only integer types

that if-else chain can typically be rewritten as a switch statement


int main() {










return 0;}


Rewrite using a switch statement!


if (op == '+') cout << (left + right) << endl; else if (op == '-') cout << (left - right) << endl; else if (op == '*') cout << (left * right) << endl; else if (op == '/') cout << (left / right) << endl; else if (op == '%') cout << (left % right) << endl; else cout << "Unknown operation" << endl;

Switch Statement

switch (op) { case '+' : cout << (left + right) << endl; break; case '-' : cout << (left - right) << endl; break; case '*' : cout << (left * right) << endl; break; case '/' : cout << (left / right) << endl; break; case '%' : cout << (left % right) << endl; break; default: cout << "Unknown operation" << endl;}


if (op == '+') cout << (left + right) << endl; else if (op == '-') cout << (left - right) << endl; else if (op == '*') cout << (left * right) << endl; else if (op == '/') cout << (left / right) << endl; else if (op == '%') cout << (left % right) << endl; else cout << "Unknown operation" << endl;

Switch Statement

switch (op) { case '+' : cout << (left + right) << endl; break; case '-' : cout << (left - right) << endl; break; case '*' : cout << (left * right) << endl; break; case '/' : cout << (left / right) << endl; break; case '%' : cout << (left % right) << endl; break; default: cout << "Unknown operation" << endl;}


int main() {




switch (op) { case '+' : cout << (left + right) << endl; break; case '-' : cout << (left - right) << endl; break; case '*' : cout << (left * right) << endl; break; case '/' : cout << (left / right) << endl; break; case '%' : cout << (left % right) << endl; break; default: cout << "Unknown operation" << endl;} return 0;}

Switch & Fall-throughwhat happens if the break statements of a

switch statement are omitted? int num; cout << "Please enter a number: "; cin >> num;

switch (num) { case 1: cout << "One" << endl; break; case 2: cout << "Two" << endl; break; case 3: cout << "Three" << endl; break; default: cout << "I can only count to three." << endl; }

Switch & Fall-through when a matching literal is found, program executes all

statements following the case statement until it finds a break statement

int num; cout << "Please enter a number: "; cin >> num;

switch (num) { case 1: cout << "One" << endl; case 2: cout << "Two" << endl; case 3: cout << "Three" << endl; default: cout << "I can only count to three." << endl; }

When user entered a 3, all statements following this case were executed.











Switch & Fall-throughwhen a break statement is omitted, the code

for another case statement is executed this is known as fall-through this is often a source of programming errorhowever, it can also be used to the

programmer's advantage

Write a program that takes in a character, and prints whether or not that character is a vowel.

Please input a character: uu is a vowel

Please input a character: tt is not a vowel

Please input a character: %% is not a vowel


int main() {

char input;

cout << "Please input a character: "; cin >> input;

switch (input) { case 'a':

cout << input << " is a vowel!" << endl; break;

case 'A': cout << input << " is a vowel!" << endl; break;

case 'e': cout << input << " is a vowel!" << endl; break;

case 'E': cout << input << " is a vowel!" << endl; break;


continued …

case 'i': cout << input << " is a vowel!" << endl; break;

case 'I': cout << input << " is a vowel!" << endl; break;

case 'o': cout << input << " is a vowel!" << endl; break;

case 'O': cout << input << " is a vowel!" << endl; break;

case 'u': cout << input << " is a vowel!" << endl; break;

case 'U': cout << input << " is a vowel!" << endl; break;

default: cout << input << " is not a vowel!" << endl;

} return 0;}



int main() {

char input;


switch (input) { case 'a': case 'A': case 'e': case 'E': case 'i': case 'I': case 'o': case 'O': case 'u': case 'U':



} return 0;}



int main() {

char input;


switch (input) { case 'a': case 'e': case 'i': case 'o': case 'u': case 'A': case 'E': case 'I': case 'O': case 'U':



} return 0;}


Documents

Computer Science 1620 Selection Structures. Write a program that accepts the speed of a vehicle, and determines whether that person is speeding assume