I’m writing calculator that calculates values from expressions:
3 (23/24)*34/24
I used RPN algorithm: https://en.wikipedia.org/wiki/Reverse_Polish_notation
I have now sorted expression in String:
3 23 24 / 34 * 24 /
I don't have any idea how can I get value from this expression.
Thx
CodePudding user response：
The basic idea behind RPN is that there is a stack that all the arguments get put on, then taken off for an operation.
For this set, the basic flow will be:
| Element | Stack | a | b |
|---|---|---|---|
| push 3 | 3 | ||
| push 23 | 3,23 | ||
| push 24 | 3,23,24 | ||
| -divide | |||
| pop b | 3,23 | 24 | |
| pop a | 3 | 23 | 24 |
| push a/b | 3, 0.9583 | ||
| end-divide | |||
| push 34 | 3, 0.9583, 34 | ||
| -multiply | |||
| pop b | 3, 0.9583 | 34 | |
| pop a | 3 | 0.9583 | 34 |
| push a*b | 3, 32.5833 | ||
| end-multiply | |||
| push 24 | 3, 32.5833, 24 | ||
| -divide | |||
| pop b | 3, 32.5833 | 24 | |
| pop a | 3 | 32.5833 | 24 |
| push a/b | 3, 1.3576 | ||
| end-divide | |||
| add | |||
| pop b | 3 | 1.3576 | |
| pop a | 3 | 1.3576 | |
| push a b | 4.3576 | ||
| end-add |
pop solution!
CodePudding user response：
The basic algorithm is based on a stack-like structure
For each token in the expression:
- if it is a number: push it
- if it is a symbol: pop 2 values; do the matched operation; push the result
E.g.:
"3 23 24 / 34 * 24 / "
Stack
3: push 3 | 3
23: push 23 | 3 23
24: push 24 | 3 23 24
/: pop (24), pop (23), push 23/24 | 3 0.95
34: push 34 | 3 0.95 34
*: pop (34), pop (0.95), push 0.95*34 | 3 32.58
24: push 24 | 3 32.58 24
/: pop (24), pop (32.58), push 32.58/24 | 3 1.35
: pop (1.35), pop (3), push 3 1.35 | 4.35
The last value that remains in the stack is the result