Using our stack in a Reverse Polish Calculator, continued
Careful readers may have noticed that in some cases
we don't actually need the integer variables val1 and val2.
We can use the 2 results returned from pop_item
as arguments to push_item:
int evaluate_RPN(FILE *fp)
{
char line[BUFSIZ];
while( fgets(line, sizeof line, fp) != NULL ) {
if(line[0] == '#')
continue;
if(isdigit(line[0]) || line[0] == '-')
push_item( atoi(line) );
else if(line[0] == 'a') {
push_item( pop_item() + pop_item() );
}
....
}
return pop_item();
}
int main(int argc, char *argv[])
{
printf("%i\n", evaluate_RPN( stdin ) );
return 0;
}
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CITS2002 Systems Programming, Lecture 19, p7, 3rd October 2023.
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CITS2002