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9.7 Summary

In this chapter we have seen that, in C, the concept of an array can be extended to arrays of multi-dimensions. In particular, a two dimensional array is represented as a one dimensional array, each of whose elements, themselves, are one dimensional arrays, i.e. and array or arrays. Similarly, a three dimensional array is an array whose elements are each 2 dimensional arrays (an array of arrays of arrays). We have seen how such arrays are declared within programs and how they are organized in memory (row major order). We have seen how we can access the elements of multi dimensional arrays using the subscripting notation and the correspondence between this notation and pointer values. Because for higher dimensional arrays, the pointer expressions may get complicated and confusing, in general, most programs use the subscripting notations for arrays of two dimensions or more. We have also shown that when passing arrays to functions, the size of all dimensions beyond the first must be specified in the formal parameter list of the function so that the location of all elements can be calculated by the compiler.

Throughout the chapter we have seen applications for which a two dimensional data structure provides a convenient and compact way of organizing information. These have included data base applications, such as our payroll and student test score examples, as well as using two dimensional arrays to store an array of strings. We have seen how we can then use this later data structure to search and sort arrays of strings, and have shown that for this data type, as well as other large data types, it is often more efficient to work with arrays of pointers when reordering such data structures.

Finally, we have developed a rather large application using 2D arrays - solutions to simultaneous linear equations usinf Gaussian elimination. This is one algorithm for doing computations in the realm of linear algebra; several additional examples common in engineering problems are presented in Chapter .

One last point to remember about multi-dimensional arrays: this data structure is a very useful way to organize a large collection of data into one common data structure; however, all of the data items in this structure must be of the same type. In the next chapter we will see another compound data type provided in C which does not have such a restriction - the structure.