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C++ Basics: Fix the Mistake

Practice identifying and correcting common C++ beginner mistakes in syntax, variables, operators, and output with simple debugging exercises.

Instructions

For each question:

Read the problem statement.
Examine the given code carefully.
Identify the mistake or mistakes.
Explain why the code is incorrect.
Correct the code.
Compile and run the corrected program.
Explain how your correction solves the problem.

Important: Try to find the mistake yourself before checking the solution.

Question 1: Missing Semicolon

Task: Find and fix the mistake in the following program.

Incorrect Code

#include <iostream>
using namespace std;

int main()
{
    cout << "Hello World"

    return 0;
}

Question 2: Incorrect Data Type

Task: The program should store and display a student’s age.

Incorrect Code

#include <iostream>
using namespace std;

int main()
{
    string age = 20;

    cout << "Age: " << age << endl;

    return 0;
}

Question 3: Incorrect Variable Assignment

Task: The program should store a student’s marks as a decimal value.

Incorrect Code

#include <iostream>
using namespace std;

int main()
{
    float marks;
    marks = "85.5";

    cout << "Marks: " << marks << endl;

    return 0;
}

Question 4: Incorrect Character Declaration

Task: The program should store and display a student’s grade.

Incorrect Code

#include <iostream>
using namespace std;

int main()
{
    char grade = "A";

    cout << "Grade: " << grade << endl;

    return 0;
}

Question 5: Incorrect Integer Declaration

Task: The program should store the number of students in a classroom.

Incorrect Code

#include <iostream>
using namespace std;

int main()
{
    float students = 45.5;

    cout << "Total Students: " << students << endl;

    return 0;
}

Question 6: Missing Header File

Task: The program should store and display a student’s name.

Incorrect Code

#include <iostream>
using namespace std;

int main()
{
    string name = "Ali";

    cout << "Student Name: " << name << endl;

    return 0;
}

Question 7: Incorrect Data Type for Average

Task: The program should calculate the average of three numbers and display the decimal result.

Incorrect Code

#include <iostream>
using namespace std;

int main()
{
    int a = 10;
    int b = 15;
    int c = 20;

    int average = (a + b + c) / 3.0;

    cout << "Average: " << average << endl;

    return 0;
}

Question 8: Incorrect Data Types for Student Information

Task: The program should store a student’s name, age, and percentage.

Incorrect Code

#include <iostream>
#include <string>
using namespace std;

int main()
{
    int name = "Ahmed";
    string age = "20";
    int percentage = 85.75;

    cout << name << endl;
    cout << age << endl;
    cout << percentage << endl;

    return 0;
}

Question 9: Incorrect Data Type for Distance

Task: The program should store the distance between two cities in kilometres, including decimal values.

Incorrect Code

#include <iostream>
using namespace std;

int main()
{
    int distance = 125.75;

    cout << "Distance: " << distance << " km" << endl;

    return 0;
}

Question 10: Incorrect Data Type for Boolean

Task: The program should store and display whether a student is enrolled or not.

Incorrect Code

#include <iostream>
using namespace std;

int main()
{
    int isEnrolled = true;

    cout << "Enrollment Status: " << boolalpha
         << isEnrolled << endl;

    return 0;
}

Question 11: Incorrect Data Type in Calculation

Task: The program should calculate the total price of three items, where each item costs 45.75.

Incorrect Code

#include <iostream>
using namespace std;

int main()
{
    int price = 45.75;
    int quantity = 3;

    int total = price * quantity;

    cout << "Total Price: " << total << endl;

    return 0;
}

Question 12: Incorrect Assignment Operator

Task: The program should increase the value of a number by 5.

Incorrect Code

#include <iostream>
using namespace std;

int main()
{
    int number = 10;

    number + 5;

    cout << "Number: " << number << endl;

    return 0;
}

Question 13: Incorrect Multiplication Operator

Task: The program should calculate the product of two numbers.

Incorrect Code

#include <iostream>
using namespace std;

int main()
{
    int a = 8;
    int b = 5;

    int product = a + b;

    cout << "Product: " << product << endl;

    return 0;
}

Question 14: Incorrect Modulus Operator

Task: The program should calculate the remainder when 17 is divided by 5.

Incorrect Code

#include <iostream>
using namespace std;

int main()
{
    int a = 17;
    int b = 5;

    int remainder = a / b;

    cout << "Remainder: " << remainder << endl;

    return 0;
}

Question 15: Incorrect Increment Operator

Task: The program should increase a number by one using the increment operator.

Incorrect Code

#include <iostream>
using namespace std;

int main()
{
    int number = 10;

    number--;

    cout << "Number: " << number << endl;

    return 0;
}

Question 16: Incorrect Calculation Order

Task: The program should add two numbers first and then multiply the sum by 3.

Incorrect Code

#include <iostream>
using namespace std;

int main()
{
    int a = 5;
    int b = 10;

    int result = a + b * 3;

    cout << "Result: " << result << endl;

    return 0;
}

Question 17: Incorrect Average Calculation

Task: The program should calculate the average of three numbers.

Incorrect Code

#include <iostream>
using namespace std;

int main()
{
    int a = 10;
    int b = 20;
    int c = 30;

    int average = a + b + c / 3;

    cout << "Average: " << average << endl;

    return 0;
}

Question 18: Incorrect Multiplication and Addition

Task: The program should multiply two numbers first and then add 10 to the result.

Incorrect Code

#include <iostream>
using namespace std;

int main()
{
    int a = 5;
    int b = 4;

    int result = a + b * 10;

    cout << "Result: " << result << endl;

    return 0;
}

Question 19: Incorrect Division and Subtraction

Task: The program should subtract 5 from 20 and then divide the result by 3.

Incorrect Code

#include <iostream>
using namespace std;

int main()
{
    int a = 20;
    int b = 5;
    int c = 3;

    int result = a - b / c;

    cout << "Result: " << result << endl;

    return 0;
}

Question 20: Incorrect Mathematical Expression

Task: The program should calculate the product of the sum of a and b and the difference of c and d.

Incorrect Code

#include <iostream>
using namespace std;

int main()
{
    int a = 5;
    int b = 3;
    int c = 10;
    int d = 4;

    int result = a + b * c - d;

    cout << "Result: " << result << endl;

    return 0;
}

Question 21: Incorrect Expression with Modulus

Task: The program should calculate the remainder of the sum of two numbers divided by 5.

Incorrect Code

#include <iostream>
using namespace std;

int main()
{
    int a = 7;
    int b = 8;

    int result = a + b % 5;

    cout << "Remainder: " << result << endl;

    return 0;
}

Question 22: Incorrect Expression with Multiple Operators

Task: The program should calculate:

\[ (a+b)\times 2-c \]

Incorrect Code

#include <iostream>
using namespace std;

int main()
{
    int a = 4;
    int b = 6;
    int c = 5;

    int result = a + b * 2 - c;

    cout << "Result: " << result << endl;

    return 0;
}

Question 23: Incorrect Percentage Calculation

Task: The program should calculate the percentage obtained by a student.

Incorrect Code

#include <iostream>
using namespace std;

int main()
{
    int obtained = 400;
    int total = 500;

    double percentage = obtained / total * 100;

    cout << "Percentage: " << percentage << "%" << endl;

    return 0;
}

Question 24: Missing Constant Initialization

Task: The program should declare a constant for PI and display its value.

Incorrect Code

#include <iostream>
using namespace std;

int main()
{
    const double PI;

    PI = 3.14159;

    cout << "PI: " << PI << endl;

    return 0;
}

Question 25: Changing a Constant

Task: The program should calculate the area of a square using a constant side length.

Incorrect Code

#include <iostream>
using namespace std;

int main()
{
    const int SIDE = 5;

    SIDE = 10;

    int area = SIDE * SIDE;

    cout << "Area: " << area << endl;

    return 0;
}

Question 26:

Task: The program should declare the value of a week as a constant and display the number of days.

Incorrect Code

#include <iostream>
using namespace std;

int main()
{
    int DAYS_IN_WEEK = 7;

    cout << "Days in a week: "
         << DAYS_IN_WEEK << endl;

    return 0;
}

Question 27: Changing Constant During Calculation

Task: The program should calculate the total price of five items using a constant item price.

Incorrect Code

#include <iostream>
using namespace std;

int main()
{
    const double PRICE = 150.50;
    int quantity = 5;

    PRICE = PRICE * quantity;

    cout << "Total Price: " << PRICE << endl;

    return 0;
}

Question 28: Incorrect Constant Initialization

Task: The program should calculate the circumference of a circle using a constant PI value.

Incorrect Code

#include <iostream>
using namespace std;

int main()
{
    const double PI = 3.14159;
    double radius = 5;

    const double circumference;

    circumference = 2 * PI * radius;

    cout << "Circumference: "
         << circumference << endl;

    return 0;
}

Question 29: Integer Division

Task: The program should divide two integer numbers and display the decimal result.

Incorrect Code

#include <iostream>
using namespace std;

int main()
{
    int a = 7;
    int b = 2;

    double result = a / b;

    cout << "Result: " << result << endl;

    return 0;
}

Question 30: Incorrect Type Conversion

Task: The program should convert an integer value into a decimal value.

Incorrect Code

#include <iostream>
using namespace std;

int main()
{
    int number = 15;

    double result = int(number / 2);

    cout << "Result: " << result << endl;

    return 0;
}

Question 31: Incorrect Character Conversion

Task: The program should convert an integer ASCII code into its corresponding character.

Incorrect Code

#include <iostream>
using namespace std;

int main()
{
    int code = 65;

    int character = char(code);

    cout << "Character: " << character << endl;

    return 0;
}

Question 32: Missing Type Casting in Average

Task: The program should calculate the average of three integers and display the decimal result.

Incorrect Code

#include <iostream>
using namespace std;

int main()
{
    int a = 10;
    int b = 20;
    int c = 25;

    double average = (a + b + c) / 3;

    cout << "Average: " << average << endl;

    return 0;
}

Question 33: Incorrect Type Casting Position

Task: The program should calculate the average of three numbers using type casting.

Incorrect Code

#include <iostream>
using namespace std;

int main()
{
    int a = 10;
    int b = 20;
    int c = 25;

    double average = double(a + b + c / 3);

    cout << "Average: " << average << endl;

    return 0;
}