How do I know how many loops to use with arrays in C?

A useful way to learn is to trace a small array by hand. Write down the indices and follow each loop iteration one at a time. This makes it easier to see which row and column are being accessed, instead of trying to understand everything at once. Books such as C: A Modern Approach and free introductory C courses can also provide extra practice.

Think of a two-dimensional array as a table. The first index selects a row and the second selects a column, such as array[row][column]. To process every value, use an outer loop for the rows and an inner loop for the columns.

It depends on what you’re trying to do. A one-dimensional array usually needs one loop when you want to visit every element. A two-dimensional array commonly needs two nested loops: one for the rows and one for the columns. The exact number can vary depending on the operation, so a specific problem would make the answer clearer.

For example, suppose you have temperature readings for three mountains, with six readings per mountain: double temperatures[3][6]. You can visit every reading like this: for (int mountain = 0; mountain < 3; ++mountain) { for (int time = 0; time < 6; ++time) { double temperature = temperatures[mountain][time]; /* process it */ } } The outer loop handles the first dimension, and the inner loop handles the second.