Here come the general/special purpose equation/function calculator!
Students, scientists, accountants, merchants, anyone can easily use it for a instant result.

Usage:
-equation string, e.g. 1+2x3-4÷5.0-.2+1+2^5 = 39

-VAT % calculation, e.g. 7 % x 56000 = 3,920

-Auto Floating point operation, e.g. 11÷2 = 5.5
11.0÷2 = 5.5
11÷2.0 = 5.5

-compound operators and precedence +, -, x, ÷, ^, e.g. 1+2x3÷4-5 = -2.5
1+2x3÷4.0-5 = -2.5
2^10 = 1024

-use parenthesis ( ) as highest operator precedence. e.g. (3+6)x2-3÷2 = 16.5

-always use parenthesis to prevent ambiguity, e.g. √9+2 means √11, to get √9 plus 2, equation must be (√9)+2, result: (√9)+2 = 5

-perform x^y, e.g.2^16 = 65,536

-perform square root, e.g. tap √ , tap 6 2 5, tap = , result: √625 = 25

-compute %, e.g. to compute 5% of 300. Tap 5, tap %, tap x, tap 3 0 0, tap =, result: 0.05x300 = 15

-compute logarithm base 10, e.g. to compute log1000, Tap log, tap 1 000, tap =, result: log1000 = 3

-equation log100+10 means log110, to compute log100 plus 10, equation must be (log100)+10, result: (log100)+10 = 12

-compute natural logarithm base e, e.g. ln2, Tap ln, tap 2, tap =, result: ln2 = 0.693147

-compute factorial, e.g. 5!, Tap 5, tap !, result: 5! = 120

-compute inverse of x or 1/x, e.g. 1/25, Tap 25, tap 1/x, result: 1/25 = 0.04

-compute area of a circle with radius 5, e.g. Tap 2, tap x, tap Pi, tap x, tap 5, tap =, result: 2xPix5 = 31.4159

-Continuous computation, e.g. to compute 7.5% of 800 then add by 1000. Tap 7.5, tap %, tap x, tap 800, tap +, tap 1 000, tap =, result: 0.075x800+1000 = 1060

-Tap share button to share the result of the computation to other apps.

-Tap M+ to add result in memory, 
-Tap M- to subtract result in memory, 
-Tap MR to recall result from memory.
-Tap MC to clear result from memory.

-Tap hist button to to view and select the previous calculation history.

-long press equation or result label to copy/paste equation and/or result to/from other app, e.g. 17.0+2x3-4x5÷6+7-8x9÷5+6x7-5 = 49.266667

-Tap speaker On/Off button to toggle button click sound.

Note:
-Operators (, ), +, -, x, ÷, and ^ can combine into a long equation string. e.g. 17+2x3^2-4x5÷6.0+(7-8)x9÷5.0+6x7-5 = 66.866667

-Computation follows operator precedence, e.g. 1+2x3-2^3+1 = 0
2x(3+4)÷3.0+5 = 9.666667

-Operators !, % and 1/x can only be used in a single operation or first operator in mixed operation. e.g. 5!, 6%, but not 2 + 5!, not 20 + 5%.
-but can use as first operator. e.g. 5! + 2, or 5% + 20.

-Mod operator can not be mixed with other operators. To compute 34 mod 5. Tap 3 4, tap Mod, tap 5, tap =, result: 34 Mod 5 = 4

Invalid equation:
2√9 must change to 2x√9
2log100 must change to 2xlog100
2Pi5 must change to 2xPix5
In equation, multiplication must always use x operator.