Nested loops are a powerful tool in C# programming, allowing you to repeat one set of instructions inside another. This structure is especially useful when you need to work with multi-dimensional data or generate complex output patterns. In C#, a nested loop is simply a loop placed inside the body of another loop. The outer loop controls the number of times the inner loop runs, and together they create a grid-like execution flow. Visualizing this, you can imagine the outer loop as rows and the inner loop as columns, much like a table. Each time the outer loop runs once, the inner loop completes all its iterations. This structure forms the basis for generating patterns such as triangles, rectangles, and more intricate shapes.

In the previous example, you see two for loops: the outer loop keeps track of the current row, and the inner loop prints the correct number of asterisks on that row. The outer loop runs from 1 to the number of rows (5 in this case), and for each iteration, the inner loop prints as many asterisks as the current row number. After the inner loop finishes, System.Console.WriteLine() moves the cursor to the next line, preparing for the next row. By breaking down the logic, you can see how the inner loop "builds" each row, while the outer loop moves down to the next one. This interaction between the loops is what allows you to create patterns that grow or shrink in a controlled way.

Nested loops are not limited to creating patterns on the console. In real-world programming, you often use them to process two-dimensional arrays, handle tabular data, or draw graphics in applications. For example, you might loop over rows and columns in a spreadsheet, or iterate through pixels in an image. Understanding how inner and outer loops interact is critical for tasks such as sorting tables, searching for values in grids, or simulating board games. However, it's important to use nested loops carefully, as the number of total iterations grows quickly and can impact performance in large datasets.