Arrays & Strings

1. Understanding Arrays

An array is a collection of elements of the same data type stored in contiguous memory locations. Arrays provide an efficient way to store multiple values of the same type under a single variable name. Each element in an array can be accessed using an index, which starts from 0 in C++.

Arrays are particularly useful when you need to work with a fixed number of elements of the same type. For example, storing scores of 50 students, temperatures for 7 days of the week, or coordinates for a 3D point. The contiguous memory allocation makes arrays very efficient for iteration and random access operations.

One important characteristic of arrays in C++ is that their size must be known at compile time (for static arrays). This means you cannot resize an array after it's been declared. However, C++ also provides dynamic arrays and the Standard Template Library (STL) containers like vector for more flexible array-like structures.

Declaration and Initialization

#include <iostream>
using namespace std;

int main() {
    // Declaration
    int arr[5];
    
    // Initialization
    int arr1[5] = {1, 2, 3, 4, 5};
    int arr2[] = {10, 20, 30};  // Size determined automatically
    int arr3[5] = {1, 2};  // Remaining elements are 0
    
    // Accessing elements
    cout << arr1[0] << endl;  // First element
    cout << arr1[4] << endl;  // Last element
    
    return 0;
}

Array Operations

#include <iostream>
using namespace std;

int main() {
    int arr[5] = {10, 20, 30, 40, 50};
    
    // Traversing array
    for (int i = 0; i < 5; i++) {
        cout << arr[i] << " ";
    }
    cout << endl;
    
    // Finding sum
    int sum = 0;
    for (int i = 0; i < 5; i++) {
        sum += arr[i];
    }
    cout << "Sum: " << sum << endl;
    
    // Finding maximum
    int max = arr[0];
    for (int i = 1; i < 5; i++) {
        if (arr[i] > max) {
            max = arr[i];
        }
    }
    cout << "Maximum: " << max << endl;
    
    return 0;
}

2. Multidimensional Arrays

2D Arrays

#include <iostream>
using namespace std;

int main() {
    // Declaration and initialization
    int matrix[3][3] = {
        {1, 2, 3},
        {4, 5, 6},
        {7, 8, 9}
    };
    
    // Accessing elements
    cout << matrix[0][0] << endl;  // 1
    cout << matrix[2][2] << endl;  // 9
    
    // Traversing 2D array
    for (int i = 0; i < 3; i++) {
        for (int j = 0; j < 3; j++) {
            cout << matrix[i][j] << " ";
        }
        cout << endl;
    }
    
    return 0;
}

3D Arrays

#include <iostream>
using namespace std;

int main() {
    int arr[2][3][4];  // 2 pages, 3 rows, 4 columns
    
    // Initialization
    int value = 1;
    for (int i = 0; i < 2; i++) {
        for (int j = 0; j < 3; j++) {
            for (int k = 0; k < 4; k++) {
                arr[i][j][k] = value++;
            }
        }
    }
    
    return 0;
}

3. Arrays and Functions

#include <iostream>
using namespace std;

// Passing array to function
void printArray(int arr[], int size) {
    for (int i = 0; i < size; i++) {
        cout << arr[i] << " ";
    }
    cout << endl;
}

// Modifying array in function
void doubleArray(int arr[], int size) {
    for (int i = 0; i < size; i++) {
        arr[i] *= 2;
    }
}

int main() {
    int arr[5] = {1, 2, 3, 4, 5};
    printArray(arr, 5);
    doubleArray(arr, 5);
    printArray(arr, 5);
    return 0;
}

4. C-style Strings

Character arrays terminated by null character ('\\0'):

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

int main() {
    // Declaration
    char str1[20] = "Hello";
    char str2[] = "World";
    char str3[10];
    
    // Input
    cin >> str3;  // Reads until whitespace
    cin.getline(str3, 10);  // Reads entire line
    
    // String functions
    cout << strlen(str1) << endl;  // Length: 5
    strcpy(str3, str1);  // Copy
    strcat(str1, str2);  // Concatenate
    cout << strcmp(str1, str2) << endl;  // Compare
    
    return 0;
}

5. C++ String Class

The string class provides better string handling:

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

int main() {
    // Declaration and initialization
    string str1 = "Hello";
    string str2("World");
    string str3;
    
    // Input
    cin >> str3;  // Single word
    getline(cin, str3);  // Entire line
    
    // String operations
    cout << str1.length() << endl;  // Length
    cout << str1.size() << endl;    // Same as length()
    
    // Concatenation
    string result = str1 + " " + str2;
    cout << result << endl;
    
    // Comparison
    if (str1 == str2) {
        cout << "Equal" << endl;
    }
    
    // Accessing characters
    cout << str1[0] << endl;  // 'H'
    cout << str1.at(0) << endl;  // 'H'
    
    // Substring
    string sub = str1.substr(0, 3);  // "Hel"
    
    // Find
    int pos = str1.find("ell");  // Returns position or -1
    
    // Replace
    str1.replace(0, 2, "Hi");  // Replace 2 chars from position 0
    
    return 0;
}

6. String Functions

7. Array of Strings

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

int main() {
    // Array of strings
    string names[3] = {"Alice", "Bob", "Charlie"};
    
    for (int i = 0; i < 3; i++) {
        cout << names[i] << endl;
    }
    
    // 2D array of characters (C-style)
    char words[3][20] = {"Hello", "World", "C++"};
    
    return 0;
}

Summary

Frequently Asked Questions

Conclusion

Arrays and strings are fundamental building blocks in C++ programming that every developer must master. Arrays provide efficient storage and access for collections of data, while strings enable text manipulation and processing. Understanding both C-style strings and the C++ string class gives you flexibility to work with different codebases and choose the right tool for each situation.

The concepts covered in this guide—from basic array operations to advanced string manipulation—form the foundation for more complex data structures and algorithms. Whether you're working with simple lists of numbers or processing complex text data, the skills you've learned here will be invaluable throughout your programming career.

As you continue learning C++, remember that while arrays are powerful, the Standard Template Library (STL) provides containers like vector, list, and string that offer more safety and convenience. However, understanding arrays deeply helps you appreciate these higher-level abstractions and use them more effectively.

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