CSC295 2014S, Class 01: Introduction ==================================== _Overview_ * Preliminaries. * Admin. * About the course. * Some principles and practices. * Example: C from K and R. * Detour: A C memory problem. * Exercises: Some simple tasks. * Homework. Preliminaries ------------- ### Admin * Welcome to "Thinking in C and *nix" (or whatever the course is called in the catalog). * In the future, it will be CSC 282, Thinking in C and *nix, so I think of it that way. * I'll take attendance, mostly to help me make sure that I know everyone's name. (I have 120 students this semester, so knowing everyone is hard.) * Feel free to interrupt me at any time with questions and comments. * I tend to overplan, so we won't do everything in the outline. About the course ---------------- * Your path to competency in C and *nix. * 14 classes, Sam here for 12. * Weekly homework. * Mixture of lab, discussion, recitation, lecture. * On the Web * "Textbook" under development. Some principles and practices ----------------------------- Three primary approaches * Good programming practices * Ways of thinking like a C programmer * Ways of thinking like a *nix programmer Good programming practices * Good programmers document. For clients. For themselves. * Good programmers follow a formatting standard. We'll use GNU C. * Good programmers debug with a debugger, not with printf statements (although the occasional printf is useful) * Good programmers use a source code management system (and use it well) * Don't pollute the repo. * Don't commit non-working code to the main branch. * Good programmers test their code (usually with unit tests). * Good programmers refactor rather than cut/paste/change. Good C programmers * Know how to write macros, and how to use them in clever ways * And other aspects of the C preprocessor * Know how to use a debugger, probably gdb. $ gdb program > run CRASH > bt * Know how to compile with libraries * And to use compiler flags * Understand memory and pointers * Segment large programs into individual files * Use Make Thinking like a *nix programmer * Do things by code rather than by hand * Write small programs that they can tie together with other programs. * Use text files for data and communication. * Share Example: C from K and R ----------------------- char * fun (char *t, char *s) { while (*t++ = *s++); return t; } // fun This function copies s to to. It's mostly strcpy. It returns a pointer to the one after the end-of-string character in the result. Detour: A C memory problem -------------------------- x = malloc (...); foo (); bar (); free (x); // CRASH * Program crashes with the call to free. * Program does not crash without the call to free (but leaks memory) * foo and bar use x, but have no calls to free * Neither foo nor bar reassigns x, although they do include x[i] = .... * What might be going wrong? Exercises: Some simple tasks ---------------------------- ### Given a DOS-formatted text file (lines end with \r\n rather than just \n), convert it to a standard text file. If you know awk, you could write an awk script to do it. (less than a minute, if you know awk and use it regularly) If you know flex, you can write a flex program. (five minutes) If you program regularly in C (which we'll assume, write a C program). (five to ten minutes). int ch; while ((ch = getch()) != EOF) { if (ch != '\r') putchar (ch); } // while Two more tools: * tr - character based translation (fifteen seconds) `tr -d '\r' < dosfile > usablefile` * sed - stream editor (fifteen seconds) ### Given a standard text file, convert all uppercase letters to lowercase. * Find the Python command to do that (use a scripting language). * Write a C program. (five minutes) * Copy into LibreOffice, highlight, find appropriate menu item, copy it back, deal with the automatic translation of " to curly quotes, ... (if you're running LibreOffice and it doesn't do extra translation, less than a minute; if you're not running LibreOffice, +2 minutes) ### Given a standard text file, remove all blank spaces at the end of lines. ### Make a list of all misspelled words in a text file. ### Given a CSV file in which each line has the form LastName,FirstName,Assignment,NumericGrade find the the five highest grades on HW2 ### Given an HTML file, find the URLs of all images. In case you don't know HTML, those will typically look like `` * The `img` can have any capitalization (`img`, `IMG`, `Img`, `iMg`, etc.) * There can be other text between the `img` and the `src`. (That text cannot include a greater than sign.) * You may find it easier to start this problem by assuming that there's only one image tag on a line. * But, in the end, you should support multiple image tags on the same line. Detour: Using the Shell -------------------------- * `!!` repeat the last command * `!text` repeat the last command that starts with the given text * `!123` repeats command 123 * `!$` the last thing on the last line Some important *nix tools ------------------------- Homework -------- This will appear online some time in the near future (probably over the weekend). Repository: `https://github.com/Grinnell-CSC282/hw1` 1. Read chapter 1 of Raymond to get a deeper understanding of the *nix Philosophy. 2. Find good solutions to any of the tasks we did not solve in class. (That is, write a program or command to solve the task.) Put them in a folder with your name in the GitHub repository. 3. Make a list of *nix tools and utilities that you've found useful (or even that you've just heard of). Try to categorize and add a short description. Put them in the `tools.md` file in the repository. 4. Add some notes about what might be wrong with the C code above.