bc

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toybox	source

1975
"Basic/Bench Calculator"
started as a frontend for dc
Authors:
- Robert H. Morris (43)
- Lorinda Cherry (31)

cli

bc [OPTIONS] [FILES]

use BC_ENV_VARS env var to set cli arguments
use BC_LINE_LENGTH env var set to 0(zero) to disable wrapping
runs an interactively REPL if you just run it bare "bc"

-q	–quiet	suppreses welcome message
-l	–mathlib	enables trigonometric functions, sets scale=20
-s	–standard	forces use of POSIX bc language
-w	–warn	warn when using non-POSIX extensions

language

#!/usr/bin/bc -lq
#!/usr/bin/env -S bc -lq
#!/usr/bin/env -S BC_LINE_LENGTH=0 bc -lq
print "Hello\n" # might want that \n
quit            # needs an explicit

default scale=0, aka integer division
changing the value of scale low will accumulate rounding errors
in POSIX mode, functions and variables can only be 1 character long
"**" multi line comments
accepts bases from 2 to 36
1 is true, 0 is false

arrays

index non-negative
index start at 0(zero)
no syntax sugar for creating
no automatic length book-keeping (eg: stats is impossible)
cannot be return from a function
max length given at compile time by BC_DIM_MAX (eg: 2^24)
no support for matrices

on a different "namespace" than variables

pass by reference

define fibonacci_next (*array[], n) {
    array[n] = array[n-1] + array[n-2]
    return array[n]
}

call by reference
```
fibonacci_next(vec[])
```

functions

can receive simple variables or arrays
arguments passed by value by default

new

define foo (x) {
  auto pi=3.14 # "auto" declares pi a local variable
  print "this is 2 to the power of "; x*1; 2^x; pi*2;
  print "\n"   # ";" and/or \n to separate commands
}

stdlib

fn	arg	description
length	n	significant digits, including decimals
scale	n	significant digits, only decimals
random	-	returns a random positive? integer
read	-	reads value from stdin, returns value read
print	s,…	needs "\n", no (), takes a variadic nr of args
quit	-
sqrt	n	square root
s	n	sine of angle n given in radians
c	n	cosine of angle n given in radians
a	n	arctangent of angle n given in radians
l	n	natural logarithm
e	n	exponential of `e` to `n`
j	n,m	Bessel function of integer order `n` of `x`

variables

type is infered, not declared
undefined variables return 0
lowercase (uppercase used for bases >10)

last	last command output	.	shorthand for "last"
obase	output base	ibase	input base
scale	decimals, default=0

control flow

continue (works only with "for")
break/halt/return

if (20 > 0) { print "bigger" }
if (20 > 0) { print "bigger" } else { print "smaller" }
for (i=1; i<42; ++i) {
    print i, " | ", fibonacci(i), "\n"
}
while (1) {
}

snippets

mikepierce/GNU-bc-Functions
susca/bc-extensions
idealvin/bc
extensions.bc
scientific_constants.bc
needed to handle fractional exponents, uses e() and l()
```
define pow (b,x) { return e(x*l(b)) }
```

getting the integer part of a number

define int (x) {
    auto s;
    s=scale;
    scale=0; # temporarilly chaing the scale
    x/=1;
    scale=s; # restoring scale
    return x;
}

radians <=> degrees conversions

define radtodeg (x) { return x*(45/a(1)) }
define degtorad (x) { return x*(a(1)/45) }

pi
```
scale=10
4*a(1)
```

codebases

solve.sh

$ solve.sh "4*49+732"
$ cat /usr/local/bin/solve
  #!/bin/sh
  bc << EOF
  scale=4
  $@
  quit
  EOF

sergiosgc/AdventOfCode2021

day6 part 1

for (; i>0; i-=1) {
    n = timer[0]
    for (t=0; t<8; t+=1) timer[t] = timer[t+1]
    timer[8] = n
    timer[6] += n
}
for (i=0; i<9; i+=1) result += timer[i]
print result
print "\n"

articles

cherry82.2.png — Figure 2: Lorinda Cherry in 1982