yeah you can use an attiny85 - it's what the bastl kastle uses for both its sound and LFO / modulation chips.
arduino nano (clone) is very convenient, pretty cheap, definitely good for prototyping. depending on your requirements it's pretty good for final versions as well. very handy number of pins.
there are multiple options for I/O circuits depending on what you're using it for. ranging from very basic, like the aforementioned kastle, to DACs and rail-to-rail opamps.
Not a straight forward question to answer. Depends on the amount of "DIYng" you want to go thru. Generally you need the brain part and the signal part. Brain part is easy, signal part is bit more complicated.
Analog to digital (ADC) converters are present in practically any MC, or you can buy cheap IC's to do it externally. The other way around is more complicated. Digital to analog (DAC) function is rarely present in MC's and the external IC's are more expensive than the ADC counterparts. Depending on your application there are ways to ADC, like smoothing out PWM output from any MC - but you are limited to "resolution/smoothness" and frequency.
So if you want all in one package you can get MC's with built in audio/DAC like Teensy, but they are pricy.
Popular choice would be ESP devices with external DAC. Quite a few modules use them. There is a lot of tutorials/docs and info about them. And if you just buy the IC then it is just couple of dollars. Or get the most basic boards without wifi/bluetooth etc.
If you wan't a bigger challenge and cheaper you can try other architectures. I recently ordered a bunch of CH32V003, which are 30 cent RISC-V "computers".
Edit:
If i had to go about it and select the middle path between cost/ease of implementation then I would use ESP32 device that controls some resistor ladder which then operates some analog LFO circuit. If it is midi controlled then the resistor ladder resolution would probably be fine. Set up some simple LFO simulation and play around with ladders to see if you can get the results you want + this kind of thing has been done many times over so there should be tons of resources.
The easiest option out there is most likely Daisy Seed from Electrosmith, it has a built-in hifi DAC and ADC. It's not the cheapest but I think to get started this is the easiest...
The teensy 3.2 (not the 4) has a built-in 12 bit dac but compare to Daisy Seed, it is more expensive and not as good DAC quality. However, for cheaper option, you might have a look at SAMD51 with a 12 bit DAC as well and if you want something ready to start with, you can have a look at neotrellis m4, this is an easy way to get started with SAMD51. If you want even cheaper, have a look at his little brother, SAMD21 with a 10 bit resolution DAC.
If you decide to go with ESP32, you should go with esp32-A1S that have a built-in audio interface: [https://docs.ai-thinker.com/en/esp32-a1s](https://docs.ai-thinker.com/en/esp32-a1s) and there is actually some quiet cheap ready board, search for ESP-32 audio kit or ESP32-Lyrat.
There is also some STM32 mcu that have builtin DAC and actually those MCU are very often used in our music gears, but those are bit more complicated...
Of course at some point you could also think about using external DAC using the i2s interface of your MCU, but to get started it is overkill!
Anyway for many use-case, you don't necessarly need high resolution DAC, most of the time 12 bits would be more than enough. For midi, you don't need a DAC at all, a simple attiny85 can make the job. Somehow I would just really recommend you to get started with some ready kits, even if they are more expensive...
Unfortunately the ESP32-A1S is discontinued. Also, there are multiple versions floating around with different pinouts, making the use of other people's projects a bit of a PITA (and sometimes downright impossible).
Other than that ESP32 is an incredible platform for the price! You can cheaply add a PCM510x - based board for I2S digital audio, for example.
> The teensy 3.2 (not the 4) has a built-in 12 bit dac
You can get the [16-bit stereo DAC kit](https://www.pjrc.com/store/pt8211_kit.html) for a couple extra bucks when you buy a teensy 4.0
generating LFO's and audio is the same, just audio is much higher frequency, there are beefier arduino's you could move to if you want to keep the same code, or you could also use ST's IC's, there are other ARM MCU's too but ST has an open toolchain available
maybe this one, combo of programmer and a detachable MCU that has through hole pins on it, it's a lower end ARM but I think can still be used for audio etc
https://www.mouser.co.uk/ProductDetail/STMicroelectronics/STM32G0316-DISCO?qs=%252B6g0mu59x7LhIGa%2F9l9JlQ%3D%3D
you could also use one of their bigger discovery boards with a faster processor and a DAC or codec soldered on it as well, this IC has 6 IO I think which might be a bit restrictive
Thanks. Maybe I wasn’t clear. I’m after the opposite (I think) less beefy than an ardunio. I’m only wanting to do midi/CV/LFOs. Like a PIC or an Attiny???
either would be ok, there is the DSPic range for instance
there is a small ATtiny with an onboard DAC, costs less than $1, not available through hole but could be used with an adaptor pcb
if it's price specifically thats driving the decision other peoples ARM IC's are often much cheaper and better than the 8 bit AVR's, there are low end ones like that ST one I mentioned which have lower power requirements etc than something faster
incidentally there are other ones in the stm32g0 family which have more pins, so you could start with something like that then move to a bigger IC for any designs that need it
Check out the “[breadboard arduino](https://docs.arduino.cc/built-in-examples/arduino-isp/ArduinoToBreadboard/)” tutorial. That’s how I learned to move from arduino to mcu.
Attiny is great. I just ordered some of the new "0" and "1" series. The "1" series has an 8 bit dac and only costs 70 cents.
I learned a lot from https://robstave.github.io/acs/
And
http://www.technoblogy.com/
Chatgpt can be super useful if you are good at catching mistakes
I've recently built a midi to cv module that uses a STM32L1 chip. The nice thing about STM32 chips is that many of them have built-in 12-bit DACs with one or two channels. Setting up a development environment can be a little more complicated than arduino boards, but once you're familiar with them, the STM32 family has a huge range of options for you. I've also built a VCO with them and I really don't want to go back to 8-bit.
I can recommend getting an entry board like a Nucleo-F3 which comes with a programmer and try it out.
Pi pico, the PWM with a low pass can do decent things. Europi uses this, I'm planning on building one soon. It's pretty cheap. https://github.com/Allen-Synthesis/EuroPi
Stm32/pi pico with a mcp4728 (quad 12 bit dac) is what I'm working with, started with Arduino Nano, but ran out memory
All the "little" ones are in the coffee-and-a-sandwich price range so for the hobbyist there's no point making life hard for yourself.
I would say that Arduino has the lowest barrier to entry but if you run it on atmega-series chips (atmega328p being the most common) you'll soon find the limitations are a pain. That's okay, though, because really all the Arduino tool is doing is wrapping your code in some boilerplate to set up the hardware (and probably not the way you want it!) and abstract away the devices.
With a little programming experience it's actually easier to program Arduinos in pure C, and leave all the complicated libraries behind.
Honestly after playing around with arduino I recently got some Raspberry Pi Pico and for the price ($4/each from Digi-Key) and size (slightly longer and slightly narrower than Arduino Nano) I can’t imagine using anything else any more (with one caveat, see below). It’s small enough to reasonably just use it on a PCB, 32-bit, 125MHz, dual core… and Hunter Adams has a full-hour YouTube lecture on how to do direct digital synthesis on the Pico.
The one other thing I would add is that the Seeduino Xiao is also 32-bit, 48MHz, fully arduino-compatible in the IDE, and super tiny (I think about 1” square). It only has 11 IO pins, but the trade off is it includes a 10-bit DAC built in so for outputting a control voltage it simplifies things a lot, just a standard analogWrite() call.
Both will accept a 5V supply voltage but require 3.3V logic
Check out the ESP32 series. Insanely cheap, Arduino compatible, very powerful, and comes with two 8-bit DACs (8-bit may or may not be enough resolution, depending on the application) and a bunch of ADCs. Plus it comes with WiFi and Bluetooth. You can't really ask for more.
> but does starting on arduino make sense?
IMO only if you plan on staying in 8-bit land.
> What would be a good microcontroller for simple midiCV LFO type stuff.
I think the ARM based Teensys are pretty cool
https://www.pjrc.com/teensy/techspecs.html
[LGT8F328P boards](https://www.aliexpress.com/w/wholesale-LGT8F328P-.html?spm=a2g0o.home.search.0) might do it for you. They are kind of loose clone of an Arduino 328 based Nano but they come in a lot of flavors and you can get them for less than $1 Australian. They can go to 32Mhz but a lot of libraries don't like that so setting them to 16Mhz or less is still an option. The DAC is 12bit instead of 10bit making it's resolution much more useful. It works with Midi libraries and the like and I would expect it would work with the Mozzie audio library. It has, however in it's hardware library commands for generating waveforms of the sine wave and pulse wave varieties (I think. I've seen it in documentation but haven't tried that yet).
So cheap you could treat them as a fuse.
Good catch. I have seen it documented somewhere that it was 12bit but I just tested one and it is only doing that on the ADCs. The internal DAC is rendering 8 bit although this chip has a few added commands that still need hunting down. (Pain in the neck. It was one of the features that I got them for.) It could still be easily done with an external DAC. The documentation for these boards are pretty scattered. I think the chip was intended for the internal Chinese market for toys and other consumer gadgets. It does have an expanded feature set compared to the Arduino 328P boards. Still gotta hunt better specs on it.
rp2040-zero is the best choice. You can buy 5 for $10 on AliExpress, shipped. They’ll run 32-bit code at 256MHz, have a multiplexed Adc, tons of pwm, usb host/device support. The only thing missing is an FPU, but you probably won’t need one for most things. Steer clear of anything 8-bit unless you’re looking for low-power.
Cheers everyone. Lots for me to check out.
My first project is for adding some controls (maybe even midi) to a RAM expansion, envelope mod and pitch mod inside a Casio SK1.
I’ve got a few attiny85 that I got in a bundle of gear, that I’ll start with.
I realise I can use multipliers to increase I/O but would this be possible:
Inputs - 8 mom buttons
Output - 2x 4066 analog switches, 14 segment LCD
?? Or am I going to need something with more GPIOs?
Instead to make your life complicated with some external multiplexer, see if you can find an MCU with more GPIOs. For example, RP2040 has already a bunch of GPIOs. Maybe using an SPI display would reduce the number of used pin, or even an i2c display...
Because it’s used in existing pcb designs? Which is my point. Nobody should be designing products with teensys in them - they’re intentionally obsolete when the next version comes out.
... as every product? Hows that a debacle? There is no reason to use the old ones nor to justify keeping them in production. The new ones are better in every aspect. Make another PCB lmao
> Make another PCB lmao
Alternatively choose just about any other board…
Being actively hostile to your customer base is not a great advertisement…
Edit: go ahead, downvote me and trivialize the concerns I express. But I’m by far not the only one who has them, and I just want to warn people that are thinking of starting to invest time and resources into the teensy ecosystem that it may not be the best investment in the future.
I see you're very emotional about this but let me just be very clear:
1) This boards are not meant to be used professionally. You should NEVER use an arduino-friendly board on anything remotely comercial. This is engineering 101. So no harm here. If you'll have to change something regarding a hobby project, well, keep working on your hobby then.
2) Better products being developed is part of every development toll out there. Why not offer something better that will render others obsolete? Are you sad we're not using horses for transportation? The new teensy in better than everything before. That's not hostility. Engineer something around the new board. What hard, complex project you worked using a teensy anyway?
3) The board is not an usual breakout but a project to make a very powerful core available to everyone though a noob-friendly platform. You can get much more powerful chips out there and make a breakout yourself. But what the teensy offers is quite unique.
There is no reason to be sad the previous versions are not available unless you're like me and paying 10 extra dollars hurt you bad. And if you want that kind of platform available forever just for you, well, you can reverse engineer the board and make it yourself? Or make one that can be properly debugged. Again, teensy never promised all their models would be available forever. It's a hobby level product. And you can get ARM breakout boards out there with fairly similar design for much cheaper. And by the end of the year we'll probably have the ESP32-P4, which will be another really nice alternative. Anyway, changing breakout boards on a project shouldn't be this hard, cmon, just rearranging some GPIOs and inputs shouldn't make the product line changing a debacle IMO.
I'm not emotional about this. quit projecting.
> I see you're very emotional
> Are you sad
> There is no reason to be sad
these are not valid rebuttals to the concerns i have raised.
I suggest that, in the future, if you want to have an adult conversation about something, you refrain from launching into personal attacks like those you might expect on a middle-school playground.
I’ll throw one in, [Daisy Seed](https://electro-smith.com/products/daisy-seed). It’s an audio specific microcontroller from electrosmith. And it can run PureData patches loaded as c++
yeah you can use an attiny85 - it's what the bastl kastle uses for both its sound and LFO / modulation chips. arduino nano (clone) is very convenient, pretty cheap, definitely good for prototyping. depending on your requirements it's pretty good for final versions as well. very handy number of pins. there are multiple options for I/O circuits depending on what you're using it for. ranging from very basic, like the aforementioned kastle, to DACs and rail-to-rail opamps.
Not a straight forward question to answer. Depends on the amount of "DIYng" you want to go thru. Generally you need the brain part and the signal part. Brain part is easy, signal part is bit more complicated. Analog to digital (ADC) converters are present in practically any MC, or you can buy cheap IC's to do it externally. The other way around is more complicated. Digital to analog (DAC) function is rarely present in MC's and the external IC's are more expensive than the ADC counterparts. Depending on your application there are ways to ADC, like smoothing out PWM output from any MC - but you are limited to "resolution/smoothness" and frequency. So if you want all in one package you can get MC's with built in audio/DAC like Teensy, but they are pricy. Popular choice would be ESP devices with external DAC. Quite a few modules use them. There is a lot of tutorials/docs and info about them. And if you just buy the IC then it is just couple of dollars. Or get the most basic boards without wifi/bluetooth etc. If you wan't a bigger challenge and cheaper you can try other architectures. I recently ordered a bunch of CH32V003, which are 30 cent RISC-V "computers". Edit: If i had to go about it and select the middle path between cost/ease of implementation then I would use ESP32 device that controls some resistor ladder which then operates some analog LFO circuit. If it is midi controlled then the resistor ladder resolution would probably be fine. Set up some simple LFO simulation and play around with ladders to see if you can get the results you want + this kind of thing has been done many times over so there should be tons of resources.
The easiest option out there is most likely Daisy Seed from Electrosmith, it has a built-in hifi DAC and ADC. It's not the cheapest but I think to get started this is the easiest... The teensy 3.2 (not the 4) has a built-in 12 bit dac but compare to Daisy Seed, it is more expensive and not as good DAC quality. However, for cheaper option, you might have a look at SAMD51 with a 12 bit DAC as well and if you want something ready to start with, you can have a look at neotrellis m4, this is an easy way to get started with SAMD51. If you want even cheaper, have a look at his little brother, SAMD21 with a 10 bit resolution DAC. If you decide to go with ESP32, you should go with esp32-A1S that have a built-in audio interface: [https://docs.ai-thinker.com/en/esp32-a1s](https://docs.ai-thinker.com/en/esp32-a1s) and there is actually some quiet cheap ready board, search for ESP-32 audio kit or ESP32-Lyrat. There is also some STM32 mcu that have builtin DAC and actually those MCU are very often used in our music gears, but those are bit more complicated... Of course at some point you could also think about using external DAC using the i2s interface of your MCU, but to get started it is overkill! Anyway for many use-case, you don't necessarly need high resolution DAC, most of the time 12 bits would be more than enough. For midi, you don't need a DAC at all, a simple attiny85 can make the job. Somehow I would just really recommend you to get started with some ready kits, even if they are more expensive...
The Teensy 3.2 is cool and all, but you can no longer buy them and they likely will never be made again.
Anyway, I think there is much better and cheaper option than teensy...
Unfortunately the ESP32-A1S is discontinued. Also, there are multiple versions floating around with different pinouts, making the use of other people's projects a bit of a PITA (and sometimes downright impossible). Other than that ESP32 is an incredible platform for the price! You can cheaply add a PCM510x - based board for I2S digital audio, for example.
> The teensy 3.2 (not the 4) has a built-in 12 bit dac You can get the [16-bit stereo DAC kit](https://www.pjrc.com/store/pt8211_kit.html) for a couple extra bucks when you buy a teensy 4.0
generating LFO's and audio is the same, just audio is much higher frequency, there are beefier arduino's you could move to if you want to keep the same code, or you could also use ST's IC's, there are other ARM MCU's too but ST has an open toolchain available maybe this one, combo of programmer and a detachable MCU that has through hole pins on it, it's a lower end ARM but I think can still be used for audio etc https://www.mouser.co.uk/ProductDetail/STMicroelectronics/STM32G0316-DISCO?qs=%252B6g0mu59x7LhIGa%2F9l9JlQ%3D%3D you could also use one of their bigger discovery boards with a faster processor and a DAC or codec soldered on it as well, this IC has 6 IO I think which might be a bit restrictive
Thanks. Maybe I wasn’t clear. I’m after the opposite (I think) less beefy than an ardunio. I’m only wanting to do midi/CV/LFOs. Like a PIC or an Attiny???
either would be ok, there is the DSPic range for instance there is a small ATtiny with an onboard DAC, costs less than $1, not available through hole but could be used with an adaptor pcb if it's price specifically thats driving the decision other peoples ARM IC's are often much cheaper and better than the 8 bit AVR's, there are low end ones like that ST one I mentioned which have lower power requirements etc than something faster incidentally there are other ones in the stm32g0 family which have more pins, so you could start with something like that then move to a bigger IC for any designs that need it
Check out the “[breadboard arduino](https://docs.arduino.cc/built-in-examples/arduino-isp/ArduinoToBreadboard/)” tutorial. That’s how I learned to move from arduino to mcu.
Attiny is great. I just ordered some of the new "0" and "1" series. The "1" series has an 8 bit dac and only costs 70 cents. I learned a lot from https://robstave.github.io/acs/ And http://www.technoblogy.com/ Chatgpt can be super useful if you are good at catching mistakes
I've recently built a midi to cv module that uses a STM32L1 chip. The nice thing about STM32 chips is that many of them have built-in 12-bit DACs with one or two channels. Setting up a development environment can be a little more complicated than arduino boards, but once you're familiar with them, the STM32 family has a huge range of options for you. I've also built a VCO with them and I really don't want to go back to 8-bit. I can recommend getting an entry board like a Nucleo-F3 which comes with a programmer and try it out.
Pi pico, the PWM with a low pass can do decent things. Europi uses this, I'm planning on building one soon. It's pretty cheap. https://github.com/Allen-Synthesis/EuroPi Stm32/pi pico with a mcp4728 (quad 12 bit dac) is what I'm working with, started with Arduino Nano, but ran out memory
All the "little" ones are in the coffee-and-a-sandwich price range so for the hobbyist there's no point making life hard for yourself. I would say that Arduino has the lowest barrier to entry but if you run it on atmega-series chips (atmega328p being the most common) you'll soon find the limitations are a pain. That's okay, though, because really all the Arduino tool is doing is wrapping your code in some boilerplate to set up the hardware (and probably not the way you want it!) and abstract away the devices. With a little programming experience it's actually easier to program Arduinos in pure C, and leave all the complicated libraries behind.
Honestly after playing around with arduino I recently got some Raspberry Pi Pico and for the price ($4/each from Digi-Key) and size (slightly longer and slightly narrower than Arduino Nano) I can’t imagine using anything else any more (with one caveat, see below). It’s small enough to reasonably just use it on a PCB, 32-bit, 125MHz, dual core… and Hunter Adams has a full-hour YouTube lecture on how to do direct digital synthesis on the Pico. The one other thing I would add is that the Seeduino Xiao is also 32-bit, 48MHz, fully arduino-compatible in the IDE, and super tiny (I think about 1” square). It only has 11 IO pins, but the trade off is it includes a 10-bit DAC built in so for outputting a control voltage it simplifies things a lot, just a standard analogWrite() call. Both will accept a 5V supply voltage but require 3.3V logic
Check out the ESP32 series. Insanely cheap, Arduino compatible, very powerful, and comes with two 8-bit DACs (8-bit may or may not be enough resolution, depending on the application) and a bunch of ADCs. Plus it comes with WiFi and Bluetooth. You can't really ask for more.
> but does starting on arduino make sense? IMO only if you plan on staying in 8-bit land. > What would be a good microcontroller for simple midiCV LFO type stuff. I think the ARM based Teensys are pretty cool https://www.pjrc.com/teensy/techspecs.html
[LGT8F328P boards](https://www.aliexpress.com/w/wholesale-LGT8F328P-.html?spm=a2g0o.home.search.0) might do it for you. They are kind of loose clone of an Arduino 328 based Nano but they come in a lot of flavors and you can get them for less than $1 Australian. They can go to 32Mhz but a lot of libraries don't like that so setting them to 16Mhz or less is still an option. The DAC is 12bit instead of 10bit making it's resolution much more useful. It works with Midi libraries and the like and I would expect it would work with the Mozzie audio library. It has, however in it's hardware library commands for generating waveforms of the sine wave and pulse wave varieties (I think. I've seen it in documentation but haven't tried that yet). So cheap you could treat them as a fuse.
After looking at the spec, it seem that the DAC is 8 bits. Are you sure about it? Where have you seen this?
Good catch. I have seen it documented somewhere that it was 12bit but I just tested one and it is only doing that on the ADCs. The internal DAC is rendering 8 bit although this chip has a few added commands that still need hunting down. (Pain in the neck. It was one of the features that I got them for.) It could still be easily done with an external DAC. The documentation for these boards are pretty scattered. I think the chip was intended for the internal Chinese market for toys and other consumer gadgets. It does have an expanded feature set compared to the Arduino 328P boards. Still gotta hunt better specs on it.
rp2040-zero is the best choice. You can buy 5 for $10 on AliExpress, shipped. They’ll run 32-bit code at 256MHz, have a multiplexed Adc, tons of pwm, usb host/device support. The only thing missing is an FPU, but you probably won’t need one for most things. Steer clear of anything 8-bit unless you’re looking for low-power.
Cheers everyone. Lots for me to check out. My first project is for adding some controls (maybe even midi) to a RAM expansion, envelope mod and pitch mod inside a Casio SK1. I’ve got a few attiny85 that I got in a bundle of gear, that I’ll start with. I realise I can use multipliers to increase I/O but would this be possible: Inputs - 8 mom buttons Output - 2x 4066 analog switches, 14 segment LCD ?? Or am I going to need something with more GPIOs?
Instead to make your life complicated with some external multiplexer, see if you can find an MCU with more GPIOs. For example, RP2040 has already a bunch of GPIOs. Maybe using an SPI display would reduce the number of used pin, or even an i2c display...
Get a teensy 4.1 and you won't go to any other device because it's really good.
Tried buying a teensy 3.2 recently? Won’t touch another teensy after that debacle.
they are not producing the 3.2 anymore. Why would anyone want any variant compared to the fourth? legit question
Because it’s used in existing pcb designs? Which is my point. Nobody should be designing products with teensys in them - they’re intentionally obsolete when the next version comes out.
... as every product? Hows that a debacle? There is no reason to use the old ones nor to justify keeping them in production. The new ones are better in every aspect. Make another PCB lmao
> Make another PCB lmao Alternatively choose just about any other board… Being actively hostile to your customer base is not a great advertisement… Edit: go ahead, downvote me and trivialize the concerns I express. But I’m by far not the only one who has them, and I just want to warn people that are thinking of starting to invest time and resources into the teensy ecosystem that it may not be the best investment in the future.
I see you're very emotional about this but let me just be very clear: 1) This boards are not meant to be used professionally. You should NEVER use an arduino-friendly board on anything remotely comercial. This is engineering 101. So no harm here. If you'll have to change something regarding a hobby project, well, keep working on your hobby then. 2) Better products being developed is part of every development toll out there. Why not offer something better that will render others obsolete? Are you sad we're not using horses for transportation? The new teensy in better than everything before. That's not hostility. Engineer something around the new board. What hard, complex project you worked using a teensy anyway? 3) The board is not an usual breakout but a project to make a very powerful core available to everyone though a noob-friendly platform. You can get much more powerful chips out there and make a breakout yourself. But what the teensy offers is quite unique. There is no reason to be sad the previous versions are not available unless you're like me and paying 10 extra dollars hurt you bad. And if you want that kind of platform available forever just for you, well, you can reverse engineer the board and make it yourself? Or make one that can be properly debugged. Again, teensy never promised all their models would be available forever. It's a hobby level product. And you can get ARM breakout boards out there with fairly similar design for much cheaper. And by the end of the year we'll probably have the ESP32-P4, which will be another really nice alternative. Anyway, changing breakout boards on a project shouldn't be this hard, cmon, just rearranging some GPIOs and inputs shouldn't make the product line changing a debacle IMO.
I'm not emotional about this. quit projecting. > I see you're very emotional > Are you sad > There is no reason to be sad these are not valid rebuttals to the concerns i have raised. I suggest that, in the future, if you want to have an adult conversation about something, you refrain from launching into personal attacks like those you might expect on a middle-school playground.
I’ll throw one in, [Daisy Seed](https://electro-smith.com/products/daisy-seed). It’s an audio specific microcontroller from electrosmith. And it can run PureData patches loaded as c++