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1. The programmer wants to know whether x is from 1 to 10, including both ends. What is the bug? ``

cpp
int x = 5;
if (1 <= x <= 10) {
    cout << "in range\n";
}

``

The if needs an else branch for the case where x is 5The code is correct, because Python and C++ read a chain of comparisons the same wayThe <= should be <, so that 10 is excludedC++ reads the chain as (1 <= x) <= 10, which compares a bool with 10, so the test is always true; write x >= 1 && x <= 10

2. The programmer wants to print valid only when x is from 1 to 10, including both ends. What is the bug? ``

cpp
int x = 50;
if (x >= 1 || x <= 10) {
    cout << "valid\n";
}

``

The >= should be >, so that 1 is rejectedThe valid message needs endl instead of \nThe || should be &&, because every int is at least 1 or at most 10, so the test is always true and 50 prints validThe variable should be unsigned, so that negative values are rejected

3. What number does this program print? A die has faces from 1 to 6. ``

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

bool is_valid_roll(int roll) {
    return 1 <= roll <= 6;
}

int main() {
    vector<int> rolls = {3, 7, 0, 6, 1};
    cout << ranges::count_if(rolls, is_valid_roll) << "\n";
}

``

3205

4. Predict the output of this program. ``

cpp
#include <iostream>
using namespace std;

bool in_range(int value, int low, int high) {
    return low <= value && value <= high;
}

int main() {
    cout << boolalpha;
    cout << in_range(5, 1, 10) << " " << in_range(15, 1, 10) << " " << in_range(7, 10, 1) << "\n";
}

``

true false falsetrue false truefalse false falsetrue true false

5. True or false: the condition 0 <= x && x < 5 is true when x is 5.

True, because 5 is at least 0 and the test only checks the lower limitFalse, because the < at the upper end leaves out 5, so 5 < 5 is false and the whole && is false

Ranges