Conditions » Examples

Driver's license oracle

This example was developed throughout the entire Conditions lesson.

#include <iostream>

int main() {
	std::cout << "Welcome to the Driver's License Oracle 5500\n";

	int year_of_birth;
	std::cout << "Please enter your year of birth: ";
	std::cin >> year_of_birth;

	int num_crashes;
	std::cout << "Please enter the number of crashes you have had: \n";
	std::cin >> num_crashes;

	char license_class = 'X'; // X is chosen as a default value to signal if we miss one of our cases
	std::string illegal_reason;

	if (num_crashes < 2) {
		// Year 2022 at the moment of writing this lesson
		int age = 2022 - year_of_birth;

		if ((age >= 18 and age <= 21) or (age >= 51 and age <= 64)) {
			license_class = 'C';
		} else if (age >= 22 and age <= 30) {
			license_class = 'B';
		} else if (age >= 31 and age <= 50) {
			license_class = 'A';
		} else {
			illegal_reason = "you are not between 18 and 64 years old";
		}
	} else {
		illegal_reason = "you have " + std::to_string(num_crashes) + " accidents";
	}

	if (license_class != 'X') {
		std::cout << "You can legally get a Class " << license_class << " driver's license\n";
	} else {
		std::cout << "You cannot legally get a driver's license because " << illegal_reason << "\n";
	}
}

Interactive boolean logic calculator

#include <iostream>
#include <iomanip>
#include <string>

int main() {
    // Ask for the two boolean inputs
    std::cout << "Welcome to the Boolean Logic Calculator!\n"
              << "Please enter two values of either true or false exactly:\n";
    
    bool input_a;
    bool input_b;

    // Use std::boolalpha to accept input as either "true" or "false"
    std::cin >> std::boolalpha >> input_a >> input_b;

    // Ask for the operation
    std::cout << "\n\nNow enter a logical operation.\n"
              << "Valid options are AND, NAND, OR, NOR, XOR, XNOR (exactly):\n";

    std::string op;
    std::cin >> op;

    // Now compute the result based on op
    bool result;

    if (op == "AND") {
        result = input_a and input_b;
    } else if (op == "NAND") {
        result = not (input_a and input_b);
    } else if (op == "OR") {
        result = input_a or input_b;
    } else if (op == "NOR") {
        result = not (input_a or input_b);
    } else if (op == "XOR") {
        result = input_a != input_b; // XOR is equivalent to "not equal" for booleans
    } else if (op == "XNOR") {
        result = input_a == input_b; // XNOR is equivalent to "equals" for booleans
    } else {
        std::cout << "Error! Invalid choice. Quitting.";
        
        // Using a return statement here to gracefully end the main function,
        // which in turn quits the program.
        // The 1 signifies a failure to the operating system.
        // You will learn more about returns in the Functions chapter.
        return 1;
    }

    std::cout << std::boolalpha; // Set output to show as true/false for booleans
    std::cout << "\n\nThe answer of " << input_a << " " << op << " " << input_b << " is " << result;
}

Computing properties of numbers

#include <iostream>

int main() {
    int value1;
    bool is_value1_even;

    std::cout << "Input a number: ";
    std::cin >> value1;

    // Compute the parity (even vs odd) of the number
    if (value1 % 2 == 0) {
        is_value1_even = true;
        
        std::cout << "Your number is even!\n";
        if (value1 == 0) {
            // Many people are confused by the parity of zero
            std::cout << "But does zero count as an even number?\n";
        }
    } else {
        is_value1_even = false;
        std::cout << "Your number is odd!\n";
    }

    // Compute the sign of the number
    if (value1 > 0) {
        std::cout << "Your number is positive!\n";
    } else if (value1 < 0) {
        std::cout << "Your number is negative!\n";
    } else {
        std::cout << "Zero is neither positive nor negative.\n";
    }

    // Ask the user for a second number to compare
    int value2;

    std::cout << "\nNow, input a number again: ";
    std::cin >> value2;

    // Compute the relative magnitude of the second number compared to the first
    if (value1 != value2) {
        std::cout << "You entered a different number... ";

        if (value1 > value2) {
            std::cout << "And it was smaller than the previous one!\n";
        } else {
            std::cout << "And it was bigger than the previous one!\n";
        }
    } else {
        std::cout << "You entered the same number!\n";
    }

    // Now check for the "special property"
    // Your numbers are special if they are both even and their difference is divisible by seven
    int diff = value1 - value2;
    bool is_value2_even= value2 % 2 == 0;

    if (is_value1_even && is_value2_even&& (diff % 7 == 0)) {
        std::cout << "Your numbers are special!";
    }
}