What's new in 1.5.0 - New free Track 0, "First steps in programming": before you write code, 20 lessons cover programs and operating systems, bits and files, algorithms, programming languages, and bugs and debugging. Read a question, think for a moment, then tap "Show answer." - A final quiz for every track: finish a track's lessons to open a final quiz of 5 basic and 5 advanced questions, and jump from a missed question to its lesson. Track headers show your lesson progress and final quiz score. - If programming is new to you, the app now suggests starting with Track 0. - Track 6 sockets: a connect interrupted by a signal now times out as it does on macOS, and the error it leaves can be read with SO_ERROR or the next recv. Tell us about any problem through the support page.

What's new in 1.4.1 - Track 6 sockets: a socket whose connection failed now behaves as it does on macOS. After a refusal or a timeout, send returns EPIPE and raises SIGPIPE, recv returns 0, getpeername and setsockopt fail with EINVAL, and poll reports it ready right away. getsockname shows the temporary port the socket was given. - A socket whose connect was interrupted by a signal now shows as "connecting" in the "fds and kernel objects" picture. - A few terms in the English lessons read more smoothly. Tell us about any problem through the support page.

What's new in 1.4.0 - New Track 7 "C for embedded development". Drive the LEDs and buttons of a virtual microcontroller board through registers, and learn volatile and bit operations, GPIO input and debouncing, the SysTick timer, interrupts and critical sections, UART and ring buffers, flash and RAM, stack limits, fixed-point math, and state machines in 7 modules, 37 lessons, and 21 exercises. The first module, 7.1 "The world of embedded C", is free, and the rest open with the Track 7 purchase. - The board runs virtually inside the app. Step through line by line to see the LEDs and buttons, the GPIO, SysTick, and USART registers, the running interrupt handler, text going to and from the terminal, and how much stack is used on the board panel. Button presses and terminal input follow a script set in advance, and nothing touches real hardware. - In board programs, the memory map groups regions into flash and RAM. The board's stack is 2KB like a small chip's, so you can watch a big local array or deep recursion overflow it. - Assembly for board examples comes from clang -O2 for Cortex-M, so you can see register reads disappear without volatile. - There are now 319 lessons and 126 exercises. Tell us about any problem through the support page.

What's new in 1.3.0 - Start C Programming is now in English. The app, lessons, quizzes, exercises, and error explanations follow your device language, and you can change it per app in the Settings app. - New Track 6 "Systems programming". Learn fork and wait, pipes with dup2 and exec, threads with mutexes and condition variables, shared memory and semaphores, sockets, and poll, kqueue, and epoll in 8 modules, 51 lessons, and 23 exercises, then build a work queue and a chat room in the last module. The first module, 6.1 "Processes and fork", is free, and the rest open with the Track 6 purchase. - Processes, threads, pipes, and sockets run virtually inside the app. Step through line by line to see tables of processes and threads, each process's memory, fds and kernel objects such as pipes and sockets, and shared memory mappings, and pick which process or thread runs next yourself. Networking is loopback inside the app only, so nothing leaves your device. - Data races, where threads share a variable without a lock, and deadlocks, where everyone waits for everyone else, are reported right where they happen. sleep and usleep do not really wait; they count virtual time inside the app. - New appendix "Computing and the lineage of C". Read the history of computing up to C, the lineage of C, and what the standards from C89 to C23 changed in 51 lessons with pictures and photos. The whole appendix is free. - Every lesson and exercise is marked beginner, intermediate, or advanced. Intermediate and advanced lessons have more explanations and examples, and lessons gained more pictures. - Tap a track in the Purchase section of Settings to buy it right away. The byte view picks hex, decimal, binary, or characters with tabs. - Calling a library function without including its header now gives the same error as clang, and the explanation shows the header to include. - There are now 282 lessons and 105 exercises. Tell us about any problem through the support page.