Problems g pro- 5.1 Processes and threads provide a powerful structuring tool for imple would be much more complex as simple sequential programs. An at to introduce coroutines and compare them to processes. Consider this simple prob lem from [CONW63 construct that is instructive to examine is the coroutine. The purpose of this problen Read 80-column cards and print them on 125-character lines, with the followi changes. After every card image an extra blank is inserted, and every adjacent pair of asterisks (M) on a card is replaced by the character 1. a. Develop a solution to this problem as an ordinary sequential program, you find that the program is tricky to write. The interactions among the various ele of 80t ments of t 25: furthermore, the length of the card image, after conversion, will var he program are uneven because of the conversion from a length y depend and larity, n the number of double asterisk occurrences. One way to improve c minimize the potential for bugs, is to write the application as three on procedures The first procedure reads in card images, pads each image lank, and writes a stream of characters to a temporary file. After all o have been read, the second procedure reads the tempora substitution, and writes out a second temporary file. The thir stream of characters from the second temporary file and prints acters each file, does the character lines of 125 cha- b. The sequential solution is unattractive because of the overhead of 1/O and tc he corot porary files, Conway proposed a new form of programsurected by that allows the application to be written as three programs character buffers (Figure structure, th ere elationship between the called and calling procedurled pro e may execute a call from any point in the procedure etween the called and calling procedur dure is begun at its of call. The coroutine exhibits a more symmeti made, execution takes up from the last active p Because there is no sense in which a calling proce there is no return. Rather, any coroutine can pass entry point and returns to the calling proce ach active point in n which a calling procedure is "highe ith a resume command. The y Osume e first time a coroutine is invoked char rs, sp char inbuf[80 char outbuf[ 125]: void read) void squash0 while (true) while (true) READCARD (inbuf) for (int i-0,i