99 lines
2.6 KiB
Plaintext
99 lines
2.6 KiB
Plaintext
/******************************************************/
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/* This program evaluates an arithmetic expression */
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/* using recursion. It contains an expanded version */
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/* of the GNT procedure that obtains an expression */
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/* containing separate tokens. EXP then recursively */
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/* evaluates the tokens in the input line. */
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/******************************************************/
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expression:
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procedure options(main);
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%replace
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true by '1'b;
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declare
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sysin file,
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value float,
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(token character(10), line character(80)) varying
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static initial('');
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on endfile(sysin)
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stop;
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on error(1) /* conversion or signal */
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begin;
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put skip list('Invalid Input at ',token);
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token = ''; line = '';
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goto restart;
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end;
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restart:
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do while('1'b);
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put skip(3) list('Type expression: ');
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value = exp();
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put edit('Value is: ',value) (skip,a,f(10,4));
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end;
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gnt:
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procedure;
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declare
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i fixed;
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line = substr(line,length(token)+1);
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do while(true);
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if line = '' then
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get edit(line) (a);
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i = verify(line,' ');
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if i = 0 then
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line = '';
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else
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do;
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line = substr(line,i);
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i = verify(line,'0123456789.');
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if i = 0 then
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token = line;
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else
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if i = 1 then
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token = substr(line,1,1);
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else
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token = substr(line,1,i-1);
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return;
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end;
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end;
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end gnt;
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exp:
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procedure returns(float binary) recursive;
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declare x float binary;
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call gnt();
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if token = '(' then
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do;
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x = exp();
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call gnt();
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if token = '+' then
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x = x + exp();
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else
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if token = '-' then
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x = x - exp();
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else
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if token = '*' then
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x = x * exp();
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else
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if token = '/' then
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x = x / exp();
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else
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signal error(1);
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call gnt();
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if token ^= ')' then
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signal error(1);
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end;
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else
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x = token;
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return(x);
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end exp;
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end expression;
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