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first character of each line as a "cal riage control" character, which is not printed but may cause some actioJl such as a page eject or overprinting. When a textfile is used to represmt a particular device, the program must obey the conventions for us i ng that device. 

Textfiles may be accessed through the predeclared file procedures Get and Put. This can, of course, be quite cumbersome as these procedures are defined for single-~:haracter manipulation. To illustrate, suppose we have a natural number stored in a variable x and wish to write it on the file output. Note that the pattern of characters denoting the decimal representation of the \ alue will be quite different from that denoting the value written as a Roman numeral (see Program 4.9). But as we are usually interested in del imal notation, it appears sensible to offer built-in, standard, transf0nnation procedures that translate abstract numbers (from whatever I~omputer-internal representation is used) into sequences of decimal dl,gits and vice versa. 

The two predeclared procedures Read and Write are thereby extended in several ways to facilit.:tte the analysis and the formation of textfiles. 

## 12.A. The Standard Files Inpu1 and Output 

The standard textfiles Input and Output usually represent the standard I/O media of a computer s:vstem (such as the keyboard and the video display). Hence, they are the principal communication line between the computer system and Its human user. 

Because these two files an used very frequently, they are considered as "default values" in tl 	file operations when the textfile F is not explicitly indicated. That is 

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