Sometimes it's easier to pick from a numbered list then to enter a value explicitly. And sometimes you just want to limit input options to a pre-selected array of options.
In this example, we create a pseudo-array using the String Concatenate module. We enter three search terms into String Concatenate, and pad them with blank spaces so each string is exactly 12 charactes long. We pipe the output of this module into our Sub String module. Next, we use a Number Input module to enter our array index. This gets piped through a couple of Simple Math modules to calculate the offset into our pseudo-array (which is really just a big string). This offset value is then wired into the From value of our Sub String module. Our length value is always 12, because we've made sure to pad each substring out with enough blanks. Finally, the output from Sub String is wired into a Yahoo! Search module.
Pipe Web Address: http://pipes.yahoo.com/pipes_team/1FtESuNS3BG7EziETqoASA