C++ Programming Lecture Notes on Vectors

Introduction

• Discussed previous topics: Vector, Pair, Vector of Pairs
• Current topic: Nesting of Vectors
  • Nesting: Vector within Vector
  • Two concepts to cover:
    1. Array of Vectors
    2. Vector of Vectors

Array of Vectors

• Definition: An array that holds vectors.
  • Syntax: vector<data_type> array_name[size];
• Characteristics:
  • Array has a fixed size.
  • Each element of the array is a vector of a specific type.
  • Example: vector<int> V[5]; (array of 5 integer vectors)

Visualization

• Visualize as a 2D array:
  • Fixed number of rows (defined by array size).
  • Variable number of columns (each vector can have a different size).
• Accessing elements:
  • V[i][j] for accessing elements where i is the row (vector index) and j is the element index within that vector.

Example Code for Array of Vectors

1. Initialization: vector<int> V[3]; // Array of 3 integer vectors
2. Inserting Elements:
   • Use push_back on individual vectors:
   V[0].push_back(1); V[1].push_back(2); V[2].push_back(3);
3. Printing Elements:
   • Use nested loops to iterate through the array of vectors:
   for (int i = 0; i < 3; i++) { for (int j = 0; j < V[i].size(); j++) { cout << V[i][j] << " "; } cout << endl; }

Vector of Vectors

• Definition: A vector that contains other vectors.
  • Syntax: vector<vector<data_type>> vector_name;
• Characteristics:
  • Both the number of rows and columns are dynamic and not fixed.
  • Example: vector<vector<int>> V;

Example Code for Vector of Vectors

1. Initialization: vector<vector<int>> V;
2. Inserting Elements:
   • Directly push back vectors:
   V.push_back({1, 2, 3}); V.push_back({4, 5});
3. Printing Elements:
   • Use nested loops with dynamic size:
   for (int i = 0; i < V.size(); i++) { for (int j = 0; j < V[i].size(); j++) { cout << V[i][j] << " "; } cout << endl; }

Key Differences Between Array of Vectors and Vector of Vectors

• Array of Vectors:
  • Fixed size for the array (number of rows).
  • Each row can have a variable number of elements.
• Vector of Vectors:
  • Both number of rows and number of columns are dynamic.

Conclusion

• Understanding the difference between array of vectors and vector of vectors is crucial for efficient data management in C++.
• Next video will cover coding exercises based on these concepts.