为什么第三个 if else 语句永远不会执行？

Question

Why does line 17 never gets executed. I believe that it(if else statement) gets terminated as soon as it meets the first condition. If so, how to solve this problem. Are there any way to check all of the conditions?

#include <iostream>
/*
Why does the third if else statement never gets executed. I believe that 
it(if else statement) gets terminated as soon as it meets the first
condition. If so, how to solve this problem. Are there any way to check
all of the conditions?
*/

int main() //This check if you can drive a car or not
{
    int age;
    std::cout << "Enter your age: ";
    std::cin >> age;

    if (age >= 18)
        std::cout << "You can drive.\n";
    else if (age < 18)
        std::cout << "You have to be 18 to drive.\n";
    else if (age >= 80) // 80 and above should not drive
        std::cout << "You are too old to drive\n";
    
    return 0;
}

Answer 1

Your first test is for age >= 18 . Any age above 18 will pass, and none of the subsequent else if tests will even be checked. If you want this to work as intended, make sure to test age >= 80 first, so the next test only separates the groups below 80, eg:

if (age >= 80)
    std::cout << "You are too old to drive\n";
else if (age < 18)
    std::cout << "You have to be 18 to drive.\n";
else  // Don't need a final if check; the previous two checks ensure if you get here, the age is between 18 and 79 inclusive
    std::cout << "You can drive.\n";

Answer 2

It won't ever reach the age >= 80 since a value that large would always meet the requirement of age >= 18 and the else tells it to only choose one option.

You could check the over 80 condition first to make sure it gets found.

if (age >= 80) // 80 and above should not drive
    std::cout << "You are too old to drive\n";
else if (age >= 18)
    std::cout << "You can drive.\n";
else if (age < 18)
    std::cout << "You have to be 18 to drive.\n";

Or you could just add a condition to the first if statement so it won't apply to over 80.

if (age >= 18 && age < 80)
    std::cout << "You can drive.\n";
else if (age < 18)
    std::cout << "You have to be 18 to drive.\n";
else if (age >= 80) // 80 and above should not drive
    std::cout << "You are too old to drive\n";

Answer 3

If age >= 18 is false, then age < 18 is true.

So, no matter what age is, the third if will never be reached.