MATLAB is used to moderate interactions between users and the computer, as in running dialogs with users to gather information or in providing images for users to respond to by, for example, clicking points of interest. For example, it is often used with Microsoft Excel to read in data and/or write data to Excel, especially for use by non-MATLAB users. The aim is to create pseudo-data and print them out to check the formatting before saving the data to a text file. MATLAB allows for several formats for writing out and reading in data. MATLAB sometimes gives an error message to the effect that the variable called letter is undefined. Changing %d to %s solves the problem because %s tells MATLAB to display a string. By contrast, %d tells MATLAB to display integers—in this case, the integers corresponding to the letters corresponding to the letters in the name.