Arrays and Strings in C++

# CHAPTER 10

Arrays and Strings #

1. Introduction #

2. Learning Objectives #

• Declare and initialize arrays.

• Access and modify array elements using loops.

• Create multi-dimensional arrays (matrices).

• Differentiate between C-style strings and C++ std::string.

• Use built-in string methods.

3. Arrays in C++ #

Syntax: dataType arrayName[arraySize];

#include <iostream>
using namespace std;

int main() {
    // Declare and initialize an array of 5 integers
    int scores[5] = {85, 90, 78, 92, 88};

    // Access elements using the index (starts at 0!)
    cout << "First score: " << scores[0] << endl; // 85
    cout << "Third score: " << scores[2] << endl; // 78

    // Modify an element
    scores[1] = 95; 
    
    return 0;
}

4. Looping Through Arrays #

int scores[5] = {85, 90, 78, 92, 88};

// Traditional For Loop
for (int i = 0; i < 5; i++) {
    cout << scores[i] << " ";
}

// Modern C++ Range-Based For Loop (Much cleaner!)
for (int score : scores) {
    cout << score << " ";
}

5. Multidimensional Arrays #

// A 2D array with 2 rows and 3 columns
int matrix[2][3] = {
    {1, 2, 3}, // Row 0
    {4, 5, 6}  // Row 1
};

cout << matrix[1][2]; // Access Row 1, Col 2 -> prints 6

6. C-Style Strings (Character Arrays) #

char greeting[6] = {'H', 'e', 'l', 'l', 'o', '\0'};
// OR
char greeting2[] = "Hello"; // Compiler adds \0 automatically

7. Modern C++ Strings (std::string) #

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

int main() {
    string firstName = "John";
    string lastName = "Doe";
    
    // Concatenation (Joining strings)
    string fullName = firstName + " " + lastName;
    
    // Built-in methods
    cout << "Length: " << fullName.length() << endl; // Or fullName.size()
    
    // Accessing characters
    cout << "First letter: " << fullName[0] << endl;
    
    return 0;
}

8. Mini Project: Student Marks Management #

#include <iostream>
using namespace std;

int main() {
    int marks[5];
    int total = 0;

    cout << "Enter marks for 5 subjects:" << endl;
    for (int i = 0; i < 5; i++) {
        cout << "Subject " << (i + 1) << ": ";
        cin >> marks[i];
        total += marks[i];
    }

    float average = total / 5.0f;
    cout << "--- REPORT CARD ---" << endl;
    cout << "Total Marks: " << total << "/500" << endl;
    cout << "Average: " << average << "%" << endl;

    return 0;
}

9. Memory-Level Explanation #

Index:      0         1         2
Value:    [ 10 ]    [ 20 ]    [ 30 ]
Address:  0x100     0x104     0x108

The variable name arr actually holds the memory address of the first element (0x100).

10. Common Mistakes #

• Out of Bounds Error: Accessing scores[5] in a 5-element array. Valid indices are 0 to 4. C++ does NOT check array bounds; it will simply read random garbage memory or crash (Segmentation Fault).

• String Concatenation Bug: string x = "Hello" + "World"; is illegal because you can't add two raw string literals. At least one must be a std::string variable.

11. Exercises #

1. 1. Create an array of 10 integers. Use a loop to find and print the largest number in the array.

1. 2. Create a string variable. Use a loop to print the string backwards.

1. 3. Write a program using a 2D array to represent a 3x3 Tic-Tac-Toe board and print it to the screen.

12. MCQ Quiz with Answers #

13. Interview Questions #

• Q: Explain why C++ arrays do not have bounds checking, and what the consequences are.

• Q: Differentiate between a C-string (char[]) and a C++ std::string. Which is preferred and why?

• Q: How do you pass an array to a function? Does it pass by value or by reference? (Answer: By reference (pointer)).

14. Summary #

15. Next Chapter Recommendation #