Embercode: AI-powered software engineer course

1. The guard is meant to stop the read when i is 3, but it does not. What is the bug? ``

cpp
#include <iostream>
#include <vector>
using namespace std;

int main() {
    vector<int> v = {4, 0, 7};
    int i = 3;
    if (v[i] == 0 && i < static_cast<int>(v.size())) {
        cout << "zero\n";
    }
}

``

== should be !=, so the read happens only for valid slots.The read v[i] runs before the check i < size, so it reads past the end. The bounds check must come first, on the left of &&.size() must not be converted with static_cast<int>.Vector slots start at 1, so the check should be i <= size.

2. x is 5 and y is 3, so they differ, but the program prints same. What is the cause? ``

cpp
#include <iostream>
using namespace std;

int main() {
    int x = 5;
    int y = 3;
    if (x ^ y == 0) {
        cout << "same\n";
    }
}

``

^ is the power operator, so x ^ y is 5 to the power 3.y and x are both int, so the comparison == always gives true.== binds tighter than ^, so the test is x ^ (y == 0). That is 5 ^ 0, which is 5, and any nonzero value counts as true.An int cannot be used in an if, so the test is always true.

3. What does this program print? Each line is listed in order, separated by commas. ``

cpp
#include <iostream>
using namespace std;

bool check(int v) {
    cout << "check " << v << "\n";
    return v > 2;
}

int main() {
    if (check(1) && check(5)) cout << "yes\n";
    if (check(3) || check(9)) cout << "ok\n";
}

``

check 1, check 3, okcheck 1, check 5, yes, check 3, okcheck 1, yes, check 3, okcheck 1, check 5, yes, check 3, check 9, ok

4. What does this program print? ``

cpp
#include <iostream>
using namespace std;

int main() {
    int a = 9;
    int b = 4;
    a ^= b;
    b ^= a;
    a ^= b;
    cout << a << " " << b << "\n";
}

``

9 413 44 90 0

5. Type the value of x ^ x for any int x.

Type your answer.

Guards and XOR