Learning Exercise
In C++, you can compare values using the comparison operators.
| Comparison | Operator |
|---|---|
| equal | == |
| not equal | != |
| less | < |
| less or equal | <= |
| greater | > |
| greater or equal | >= |
The result of these comparisons is always a boolean value:
int a{3};
bool eq1 = a != 4; // true
bool eq2 = a > 5; // false
The operators == and != check whether a value is equal to another or not, respectively.
Here are some common examples:
bool eq3 = 2 == 3; // false, integer comparison
bool eq4 = 2.1 != 2.2; // true, float comparison
bool eq5 = "hello" == "hello"; // true, string comparison
The other operators check if one value is greater than (>), greater or equal to (>=), less than (<), and less or equal to (<=) to another value.
This kind of comparison is available for numbers and strings.
When comparing strings, the dictionary order (also known as lexicographic order) is followed.
bool eq6 = 2 > 3; // false, integer comparison
bool eq7 = 1.2 < 1.3; // true, float comparison
bool eq8 = "Hello" < "World"; // true, string comparison
Conditionals in C++ are similar to conditionals in other languages.
The underlying type of any conditional operation is the bool type, which can have the value of true or false.
Conditionals are often used as flow control mechanisms to check for various conditions.
An if statement can be used, which executes its code if the underlying condition is true like this:
std::string value{"val"};
if (value == "val") {
return "was val";
}
In scenarios involving more than one case many if statements can be chained together using the else if and else statements.
int number{33};
if (number > 0) {
return "positive";
} else if (number < 0) {
return "negative";
} else {
return "zero";
}
Since C++17 if-statements can also include a short initialization statement that can be used to initialize one or more variables for the if statement. For example:
int num{7};
if (int v{2 * num}; v > 10) {
return v;
} else {
return num;
}
// => 14
Note: any variables created in the initialization cannot be accessed after the end of the if statement.
In this exercise, you are going to write some code to help you prepare to buy a vehicle.
You have three tasks, one to determine if you need a license, one to help you choose between two vehicles, and one to estimate the acceptable price for a used vehicle.
Some vehicle kinds require a driver's license to operate them.
Assume only the kinds "car" and "truck" require a license, everything else can be operated without a license.
Implement the needs_license(kind) function that takes the kind of vehicle as a string and returns a boolean indicating whether you need a license for that kind of vehicle.
needs_license("car")
// => true
needs_license("bike")
// => false
needs_license("truck")
// => true
You evaluate your options of available vehicles.
You manage to narrow it down to two options but you need help making the final decision.
For that, implement the function choose_vehicle(option1, option2) that takes two vehicles as arguments and returns a decision that includes the option that comes first in lexicographical order.
choose_vehicle("Wuling Hongguang", "Toyota Corolla")
// => "Toyota Corolla is clearly the better choice."
choose_vehicle("Volkswagen Beetle", "Volkswagen Golf")
// => "Volkswagen Beetle is clearly the better choice."
The returned string should follow the pattern of "<CHOSEN_VEHICLE> is clearly the better choice.", where <CHOSEN_VEHICLE> is the option of choice from the passed arguments.
Now that you made a decision, you want to make sure you get a fair price at the dealership. Since you are interested in buying a used vehicle, the price depends on how old the vehicle is. For a rough estimate, assume if the vehicle is less than 3 years old, it costs 80% of the original price it had when it was brand new. If it is at least 10 years old, it costs 50%. If the vehicle is at least 3 years old but less than 10 years, it costs 70% of the original price.
Implement the calculate_resell_price(original_price, age) function that applies this logic using if, else if and else (there are other ways if you want to practice).
It takes the original price and the age of the vehicle as arguments and returns the estimated price in the dealership.
calculate_resell_price(1000, 1)
// => 800
calculate_resell_price(1000, 5)
// => 700
calculate_resell_price(1000.0, 15)
// => 500
Note: the return value is of type
double.
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