72 lines
1.7 KiB
PHP
72 lines
1.7 KiB
PHP
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/* main rpn parser and lexical analysis, part of the RPN calculator */
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#include <rational>
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#include <string>
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enum token
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{
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t_type, /* operator or token type */
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Rational: t_value, /* value, if t_type is "Number" */
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t_word[20], /* raw string */
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}
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const Number = '0'
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const EndOfExpr = '#'
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rpncalc(const string[])
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{
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new index
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new field[token]
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for ( ;; )
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{
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field = gettoken(string, index)
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switch (field[t_type])
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{
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case Number:
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push field[t_value]
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case '+':
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push pop() + pop()
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case '-':
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push - pop() + pop()
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case '*':
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push pop() * pop()
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case '/', ':':
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push 1.0 / pop() * pop()
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case EndOfExpr:
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break /* exit "for" loop */
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default:
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printf "Unknown operator '%s'\n", field[t_word]
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}
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}
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printf "Result = %r\n", pop()
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if (clearstack())
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print "Stack not empty\n", red
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}
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gettoken(const string[], &index)
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{
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/* first get the next "word" from the string */
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new word[20]
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word = strtok(string, index)
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/* then parse it */
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new field[token]
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field[t_word] = word
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if (strlen(word) == 0)
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{
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field[t_type] = EndOfExpr /* special "stop" symbol */
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field[t_value] = 0
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}
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else if ('0' <= word[0] <= '9')
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{
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field[t_type] = Number
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field[t_value] = rationalstr(word)
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}
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else
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{
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field[t_type] = word[0]
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field[t_value] = 0
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}
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return field
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}
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