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examples: vfmt calculator.v

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Charadon 2020-08-23 14:18:37 +00:00 committed by GitHub
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1 changed files with 135 additions and 134 deletions
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61
examples/mini_calculator.v
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@ -1,10 +1,9 @@
// Q: What's this?
// A: This is a mini "home-made" calculator. You may also regard it as a very elementary version of "interpreter".
import os
const (
numeric_char = [`0`,`1`,`2`,`3`,`4`,`5`,`6`,`7`,`8`,`9`,`.`,`e`,`E`]
numeric_char = [`0`, `1`, `2`, `3`, `4`, `5`, `6`, `7`, `8`, `9`, `.`, `e`, `E`]
)
// Convert expression to Reverse Polish Notation.
@ -15,53 +14,52 @@ fn expr_to_rev_pol(expr string) ?[]string {
mut stack := []string{}
mut rev_pol := []string{}
mut pos := 0
for pos<expr.len {
for pos < expr.len {
mut end_pos := pos
for end_pos<expr.len && expr[end_pos] in numeric_char {
for end_pos < expr.len && expr[end_pos] in numeric_char {
end_pos++
}
if end_pos>pos {
if end_pos > pos {
stack << expr[pos..end_pos]
pos = end_pos
}
else if end_pos==pos {
} else if end_pos == pos {
op := expr[pos].str()
match op {
'(' {
stack << op
}
'*', '/' {
for stack.len>0 && stack.last() !in ['(', '+', '-'] {
for stack.len > 0 && stack.last() !in ['(', '+', '-'] {
rev_pol << stack.last()
stack.delete(stack.len-1)
stack.delete(stack.len - 1)
}
stack << op
}
'+', '-' {
for stack.len>0 && stack.last() != '(' {
for stack.len > 0 && stack.last() != '(' {
rev_pol << stack.last()
stack.delete(stack.len-1)
stack.delete(stack.len - 1)
}
stack << op
}
')' {
for stack.len>0 && stack.last() != '(' {
for stack.len > 0 && stack.last() != '(' {
rev_pol << stack.last()
stack.delete(stack.len-1)
stack.delete(stack.len - 1)
}
stack.delete(stack.len-1)
stack.delete(stack.len - 1)
}
else {
return error('err: invalid character `${op}`')
return error('err: invalid character `$op`')
}
}
pos++
}
}
for stack.len>0 {
for stack.len > 0 {
top := stack.last()
rev_pol << top
stack.delete(stack.len-1)
stack.delete(stack.len - 1)
}
return rev_pol
}
@ -72,27 +70,31 @@ fn eval_rev_pol(rev_pol []string) ?f64 {
for item in rev_pol {
if is_num_string(item) {
stack << item.f64()
}
else {
if stack.len>=2 {
} else {
if stack.len >= 2 {
oprand_r := stack.last()
stack.delete(stack.len-1)
stack.delete(stack.len - 1)
oprand_l := stack.last()
stack.delete(stack.len-1)
stack.delete(stack.len - 1)
match item {
'+' { stack << oprand_l+oprand_r }
'-' { stack << oprand_l-oprand_r }
'*' { stack << oprand_l*oprand_r }
'+' {
stack << oprand_l + oprand_r
}
'-' {
stack << oprand_l - oprand_r
}
'*' {
stack << oprand_l * oprand_r
}
'/' {
if oprand_r == 0 {
return error('err: divide by zero')
}
stack << oprand_l/oprand_r
stack << oprand_l / oprand_r
}
else {}
}
}
else {
} else {
return error('err: invalid expression')
}
}
@ -109,10 +111,9 @@ fn is_num_string(str string) bool {
return true
}
fn main() {
println('Please enter the expression you want to calculate, e.g. 1e2+(3-2.5)*6/1.5 .')
println('Enter \'exit\' or \'EXIT\' to quit.')
println("Enter \'exit\' or \'EXIT\' to quit.")
mut expr_count := 0
for {
expr_count++