Online test on C/C++

AI悦创原创2024年2月17日大约 6 分钟...约 1798 字

This online test covers the material from weeks 14-16.

Question 1 (2 marks). Download the starter code marks_q1.cpp. This code con- tains an array of exam marks for some 4th year Physics course. Compile and run the code. The marks should be displayed on the screen. Now modify marks_q1.cpp so it finds and prints the highest and lowest mark for the course.

// Starter code for Question 1 of the online test
// g++ marks_q1.cpp -o marks_q1
// ./marks_q1

#include <iostream>

int main() 
{
  const int NumStudents = 36; // Number of students on the course 
  // List of exam marks for a 4th year Physics course:
  float marks[] = {65,68,58,67,60,77,53,53,56,42,60,69,70,69,83,62,57,63,90,54,62,58,77,57,59,54,61,51,38,72,71,46,27,48,52,71};
    
  std::cout << "Marks (" << NumStudents << "):" << std::endl;
  for (int i=0;i<NumStudents;i++) std::cout << marks[i] << std::endl; // Display the marks

  // --- YOUR CODE HERE ---
  // Q1 Find the min and max marks
  // Q2 Compute the average and standard deviation
  // Display the results

  return EXIT_SUCCESS;
}

Answer

// Starter code for Question 1 of the online test
// g++ marks_q1.cpp -o marks_q1
// ./marks_q1

#include <iostream>
#include <cmath>

int main() {
    const int NumStudents = 36; // Number of students on the course
    // List of exam marks for a 4th year Physics course:
    float marks[] = {65, 68, 58, 67, 60, 77, 53, 53, 56, 42, 60, 69, 70, 69, 83, 62, 57, 63, 90, 54, 62, 58, 77, 57, 59,
                     54, 61, 51, 38, 72, 71, 46, 27, 48, 52, 71};

    std::cout << "Marks (" << NumStudents << "):" << std::endl;
    for (int i = 0; i < NumStudents; i++) std::cout << marks[i] << std::endl; // Display the marks

    // --- YOUR CODE HERE ---
    // Q1 Find the min and max marks
    float maxMark = marks[0];
    float minMark = marks[0];

    for (int i = 1; i < NumStudents; ++i) {
        if (marks[i] > maxMark) maxMark = marks[i];
        if (marks[i] < minMark) minMark = marks[i];
    }
    std::cout << "Highest Mark: " << maxMark << std::endl;
    std::cout << "Lowest Mark: " << minMark << std::endl;
    // Q2 Compute the average and standard deviation
    // Display the results

    return EXIT_SUCCESS;
}

Question 2 (3 marks). Copy marks_q1.cpp to a new file marks_q2.cpp. Now add new functionality by also computing the average mark

$\langle M \rangle = \frac{1}{n} \sum_{i} M_i,$

and the standard deviation $\sigma$ which is the square-root of the variance

$\sigma^2 = \frac{1}{n} \sum_i (M_i - \langle M \rangle)^2$

where $M_i$ is the ith mark of the set of $n$ marks. Display both results to one decimal place.

Answer

// Starter code for Question 1 of the online test
// g++ marks_q1.cpp -o marks_q1
// ./marks_q1

#include <iostream>
#include <cmath>
#include <iomanip> // Include for std::setprecision

int main() {
    const int NumStudents = 36; // Number of students on the course
    // List of exam marks for a 4th year Physics course:
    float marks[] = {65, 68, 58, 67, 60, 77, 53, 53, 56, 42, 60, 69, 70, 69, 83, 62, 57, 63, 90, 54, 62, 58, 77, 57, 59,
                     54, 61, 51, 38, 72, 71, 46, 27, 48, 52, 71};

    std::cout << "Marks (" << NumStudents << "):" << std::endl;
    for (int i = 0; i < NumStudents; i++) std::cout << marks[i] << " "; // Display the marks
    std::cout << std::endl;

    // --- YOUR CODE HERE ---
    // Q2 Compute the average and standard deviation
    float sum = 0, mean, standardDeviation = 0;
    for (int i = 0; i < NumStudents; ++i) {
        sum += marks[i];
    }
    mean = sum / NumStudents;

    for (int i = 0; i < NumStudents; ++i) {
        standardDeviation += pow(marks[i] - mean, 2);
    }
    standardDeviation = sqrt(standardDeviation / NumStudents);
    // Display the results
    std::cout << "Average Mark: " << std::fixed << std::setprecision(1) << mean << std::endl;
    std::cout << "Standard Deviation: " << std::fixed << std::setprecision(1) << standardDeviation << std::endl;
    return EXIT_SUCCESS;
}

Question 3 (3 marks). Download the starter code marks_q3.cpp. This is iden- tical to marks_q1.cpp except that it also includes declarations for a function min_max() that computes the min/max marks and avg_std() which computes the average/standard deviation of the marks. Use your answers to questions 1 and 2 to help write the implementations of these functions in marks_q3.cpp. Compile and run the code to check it produces identical results to earlier.

// Starter code for Question 3 of the online test
// g++ marks_q3.cpp -o marks_q3
// ./marks_q3

#include <iostream>

void min_max(float marks[], int n, float& min, float& max); // Defines min and max as being pass by reference
void avg_std(float marks[], int n, float& avg, float& std); // Defines avg and std as being pass by reference

int main() 
{
  const int NumStudents = 36; // Number of students on the course 
  // List of exam marks for a 4th year Physics course:
  float marks[] = {65,68,58,67,60,77,53,53,56,42,60,69,70,69,83,62,57,63,90,54,62,58,77,57,59,54,61,51,38,72,71,46,27,48,52,71};
    
  std::cout << "Marks (" << NumStudents << "):" << std::endl;
  for (int i=0;i<NumStudents;i++) std::cout << marks[i] << std::endl; // Display the marks

  // --- YOUR CODE HERE ---
  // Call min_max() and avg_std() and display the results.

  return EXIT_SUCCESS;
}

// --- YOUR CODE HERE ---
// Write the implementation of min_max() and avg_std() here:

Answer

// Starter code for Question 3 of the online test
// g++ marks_q3.cpp -o marks_q3
// ./marks_q3

#include <iostream>
#include <cmath>

void min_max(float marks[], int n, float &min, float &max); // Defines min and max as being pass by reference
void avg_std(float marks[], int n, float &avg, float &std); // Defines avg and std as being pass by reference

int main() {
    const int NumStudents = 36; // Number of students on the course
    // List of exam marks for a 4th year Physics course:
    float marks[] = {65, 68, 58, 67, 60, 77, 53, 53, 56, 42, 60, 69, 70, 69, 83, 62, 57, 63, 90, 54, 62, 58, 77, 57, 59,
                     54, 61, 51, 38, 72, 71, 46, 27, 48, 52, 71};

    std::cout << "Marks (" << NumStudents << "):" << std::endl;
    for (int i = 0; i < NumStudents; i++) std::cout << marks[i] << std::endl; // Display the marks

    // --- YOUR CODE HERE ---
    // Call min_max() and avg_std() and display the results.
    float min, max, avg, stdDev;
    min_max(marks, NumStudents, min, max);
    avg_std(marks, NumStudents, avg, stdDev);

    std::cout << "Min Mark: " << min << ", Max Mark: " << max << std::endl;
    std::cout << "Average Mark: " << avg << ", Standard Deviation: " << stdDev << std::endl;
    return EXIT_SUCCESS;
}

// --- YOUR CODE HERE ---
// Write the implementation of min_max() and avg_std() here:
void min_max(float marks[], int n, float &min, float &max) {
    min = marks[0];
    max = marks[0];
    for (int i = 1; i < n; ++i) {
        if (marks[i] > max) max = marks[i];
        if (marks[i] < min) min = marks[i];
    }
}

void avg_std(float marks[], int n, float &avg, float &std) {
    float sum = 0, variance = 0;
    for (int i = 0; i < n; ++i) {
        sum += marks[i];
    }
    avg = sum / n;
    for (int i = 0; i < n; ++i) {
        variance += pow(marks[i] - avg, 2);
    }
    std = sqrt(variance / n);
}

Question 4 (2 marks). Download the starter code swap_q4.cpp. This code de- fines a 3 × 3 matrix in an array and computes its transposition. Complete the code by writing the implementation of the swap elements function swapf() declared. Compile and run the code to confirm it works.

// Starter code for Question 4 of the online test
// g++ swap_q4.cpp -o swap_q4
// ./swap_q4

#include <iostream>

void swapf(float& a, float& b); // Declare the swap function

int main() 
{
  const int n = 3; // Matrix dimension n x n
  float matrix[3][3] = { {1.0, 2.0, 3.0},
                         {4.0, 5.0, 6.0},
                         {7.0, 8.0, 9.0} };

  std::cout << "Before swap\n";
  for (int i=0;i<n;i++)
  {
    for (int j=0;j<n;j++) std::cout << matrix[i][j] << " ";
    std::cout << std::endl;
  }

  // Perform matrix transposition:
  for (int i=0;i<n;i++)
    for (int j=0;j<i;j++) // Only loop over off-diagonal elements
      swapf(matrix[i][j], matrix[j][i]);

  std::cout << "After swap\n";
  for (int i=0;i<n;i++)
  {
    for (int j=0;j<n;j++) std::cout << matrix[i][j] << " ";
    std::cout << std::endl;
  }

  return EXIT_SUCCESS;
}

void swapf(float& a, float& b) 
{
  // --- YOUR CODE HERE ---
}

Answer

// Starter code for Question 4 of the online test
// g++ swap_q4.cpp -o swap_q4
// ./swap_q4

#include <iostream>

void swapf(float &a, float &b); // Declare the swap function

int main() {
    const int n = 3; // Matrix dimension n x n
    float matrix[3][3] = {{1.0, 2.0, 3.0},
                          {4.0, 5.0, 6.0},
                          {7.0, 8.0, 9.0}};

    std::cout << "Before swap\n";
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) std::cout << matrix[i][j] << " ";
        std::cout << std::endl;
    }

    // Perform matrix transposition:
    for (int i = 0; i < n; i++)
        for (int j = 0; j < i; j++) // Only loop over off-diagonal elements
            swapf(matrix[i][j], matrix[j][i]);

    std::cout << "After swap\n";
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) std::cout << matrix[i][j] << " ";
        std::cout << std::endl;
    }

    return EXIT_SUCCESS;
}

void swapf(float &a, float &b) {
    float temp = a;
    a = b;
    b = temp;
}

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