calc:一个用C语言编写的简单计算器

## calc This is a simple calculator written in C. It uses `readline` to get user input. Initially written on January 25, 2021, current version: `1.5` ## Available commands Currently, `calc` supports the following commands: | Command | Description | |--------------|-----------------------------------------| | `calc` | Enter just-calculator mode (see [1]) | | `clear` | Clear the screen | | `color` | Enable colored output | | `examples` | Enable examples in help section | | `exit` | Close this program | | `flags` | Enable flags in help section | | `help` | Print help/usage | | `nocalc` | Disable just-calculator mode (see [1]) | | `nocolor` | Disable colored output | | `noexamples` | Disable examples in help section | | `noflags` | Disable flags in help section | | `operands` | Print list of operands | | `ops` | Print list of operands | | `quit` | Close this program | | `specvals` | Print [Special Values](#Special-Values) | [1]: the `calc` command is only available outside of just-calculator mode, and the `nocalc` command is only available inside just-calculator mode. ## Flags Currently, `calc` supports the following command-line flags: | Flag | Description | |------|----------------------------------| | `-c` | Enter just-calculator mode | | `-e` | Disable examples in help section | | `-f` | Disable flags in help section | | `-h` | Print help and exit | | `-m` | Disable program compilation info | | `-n` | Disable colored output | NOTE: Flag order matters! ([cefmnh]) ## Example operations | Command | Can be written as | Description | Result | |------------|-------------------|----------------------|---------------| | `1 + 1` | `1 p 1` | Addition | Returns 2 | | `1 - 1` | `1 s 1` | Subtraction | Returns 0 | | `2 * 2` | `2 t 2` | Multiplication | Returns 4 | | `4 / 2` | `4 d 2` | Division | Returns 2 | | `4 % 2` | `4 m 2` | Modulus | Returns 0 | | `1 < 16` | `1 l 16` | Bit-shifting (left) | Returns 65536 | | `4096 > 1` | `4096 r 4` | Bit-shifting (right) | Returns 2048 | *(See bit-shifting info [here](#Bit-Shifting))* ## Special Values You can (optionally) use Special Values, thanks to the `<math.h>` library. Here's a table containing the currently implemented values. | Special Value | Description | |---------------|-----------------------------| | E | The value of Euler's number | | Pi | The value of Pi | | Pi2 | Pi / 2 | | Pi4 | Pi / 4 | | 1Pi | 1 / Pi | | 2Pi | 2 / Pi | | Pisq | Pi² (Pi * Pi) | NOTE: these are case-insensitive, so don't worry about writing them all lowercase, uppercase, etc. For example: ``` calc> Pi + 2 5.1415926536 calc> piSq / pi 3.1415926536 calc> e + Pi2 4.2890781553 calc> pi4 * 1pI 0.2500000000 ``` It's also possible to just print a value/number, for example: ``` calc> pi 3.1415926536 calc> 7 7 calc> e 2.7182818285 calc> pisq 9.8696044011 calc> 3 3 ``` ## Bit Shifting In C, there are two kinds of bit-shifting: - Bit-shifting to the left (`<<`) - Bit-shifting to the right (`>>`) ___What is bit shifting?___ Bit shifting is, well, used to shift bits. In the computer world, integers are represented using 0s and 1s; For example, if we take the number `7`, it would be represented as follows: | 128 | 64 | 32 | 16 | 8 | 4 | 2 | 1 | |-----|----|----|----|---|---|---|---| | 0 | 0 | 0 | 0 | 0 | 1 | 1 | 1 | (That is `00000111` in binary; for simplicity's sake we'll just do a byte) Let's say we want to convert `30` to binary. In this case, we'll have: | 128 | 64 | 32 | 16 | 8 | 4 | 2 | 1 | |-----|----|----|----|---|---|---|---| | 0 | 0 | 0 | 1 | 1 | 1 | 1 | 0 | (`00011110` in binary) Now, let's talk about bit shifting. When we "shift a bit", it means to move the first (or last) bit one place to the right (`>>`) or to the left (`<<`). For example, I want to bit shift 7 one place to the right: | 128 | 64 | 32 | 16 | 8 | 4 | 2 | 1 | |-----|----|----|----|---|---|---|---| | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 1 | Now, the only values left are `2` and `1`, which make up `3`. Instead, let's try to do `30`: | 128 | 64 | 32 | 16 | 8 | 4 | 2 | 1 | |-----|----|----|----|---|---|---|---| | 0 | 0 | 0 | 0 | 1 | 1 | 1 | 1 | As you can see, the only digits left now are `8`, `4`, `2`, and `1`, which make up `15`. This time, let's do a bigger value, like `124`: | 128 | 64 | 32 | 16 | 8 | 4 | 2 | 1 | |-----|----|----|----|---|---|---|---| | 0 | 1 | 1 | 1 | 1 | 1 | 0 | 0 | Will become `62`: | 128 | 64 | 32 | 16 | 8 | 4 | 2 | 1 | |-----|----|----|----|---|---|---|---| | 0 | 0 | 1 | 1 | 1 | 1 | 1 | 0 | The same applies to bit-shifting to the right. Bit shifting is useful to calculate powers of 2, for example: 2^16: `1 << 16`: 65536 2^30: `1 << 30`: 2147483648 (32 bit limit) 2^31: `1 << 31`: 4294967296 (64 bit limit) ## Statically linking & building If you want to statically link `calc` to share it, make sure you have `musl`, `musl-gcc`, and a copy of the source code of `libreadline` and `libncurses` (needed by `libreadline`). After you've met all of the requirements, run the following: ```bash cd path/to/calc mkdir -p libs/{readline-src,readline,ncurses-src,ncurses} cd libs mv /path/to/libreadline readline-src mv /path/to/libncurses ncurses-src cd readline-src ./configure --prefix=../readline CC=musl-gcc && make -kj$(nproc) && make install-static cd ../ncurses-src ./configure --prefix=../ncurses CC=musl-gcc && make -kj$(nproc) && make install cd ../.. make static-deb ``` It should compile succesfully; When compiling `static-deb` with `make`, the output should look like this: ```bash [STATIC DEBUG] gcc: warning: ./libs/readline/lib/libreadline.a: linker input file unused because linking not done gcc: warning: ./libs/ncurses/lib/libncurses.a: linker input file unused because linking not done CC calc.c CC calc-debstatic.o ``` ## Why was this written? This was written because I was tired of using the slow Python as a command-line calculator. I wanted something fast, that I could modify whenever I wanted to. So, I quickly started writing the barebones of the calculator. It's nothing fancy, really, but a nice tool to have. More features might be added, if necessary. For any help, either: - Create an issue; - Open a pull request; - Send me an email [(saloniamatteo@pm.me)](mailto:saloniamatteo@pm.me).