as the title says, what is a way to evaluate rpn- eg this statement(5, 5, 54, /, +,) how would I evaluate it into an answer? no need figured it out
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Lots written about that on internet.
Show some code.
Well first decide on the method - shunting yard, RDP (recursive descent parser) etc.
@seeplus i already did, i got the statement into rpn
| I got the statement into RPN |
The hard part is behind you.
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#include <iostream>
struct token
{
union { double x; char o; };
bool is_number;
token(double x): x(x), is_number(true) {}
token(char o): o(o), is_number(false) {}
};
int main()
{
token expr[] = { 4.0, 3.0, 2.0, '+', '*', 3.0, 1.5, '/', '/', 0.1, '+' };
token const* const begin = expr;
token const* const end = expr + (sizeof(expr) / sizeof(*expr));
token* next = expr;
token* top = expr;
struct underflow_exception {};
auto const pop_operand = [&]{ return top == begin? throw underflow_exception{}: (--top)->x; };
for ( ;; ++next, ++top )
{
while (next != end && next->is_number) *top++ = *next++;
if (next == end) break;
double const op2 = pop_operand();
double const op1 = pop_operand();
if (next->o == '/') *top = op1 / op2;
if (next->o == '+') *top = op1 + op2;
if (next->o == '-') *top = op1 - op2;
if (next->o == '*') *top = op1 * op2;
}
std::cout << std::fixed << pop_operand() << '\n';
}
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oh @mbozzi, i h already did it, i was just replying to the guy after I finished it but thanks
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