The posted code seems incomplete or at least has some unused (like end, which if it represents the length of string could be used in place of the following repeated strlen(input)) or meaningless (like s2) variables.
I can't understand the logic behind your "Vinculum" implementation, but the simple
roman += s1; // Where s1 = value(input[i]);
It's clearly not enough to parse a roman number, where the relative position of each symbol is important. Consider e.g. "IV", which is 4 (= 5 - 1), vs. "VI", which is 6 (= 5 + 1).
To parse the "subtractive" notation, you could store a partial result and compare the current digit to the previous one. Something like the following:
#include <stdio.h>
#include <string.h>
int value_of(char ch);
long decimal_from_roman(char const *str, size_t length)
{
long number = 0, partial = 0;
int value = 0, last_value = 0;
for (size_t i = 0; i < length; ++i)
{
if (str[i] == '-')
{
number += partial;
number *= 1000;
partial = 0;
continue;
}
last_value = value;
value = value_of(str[i]);
if (value == 0)
{
fprintf(stderr, "Wrong format.\n");
return 0;
}
if (value > last_value)
{
partial = value - partial;
}
else if (value < last_value)
{
number += partial;
partial = value;
}
else
{
partial += value;
}
}
return number + partial;
}
int main(void)
{
char const *tests[] = {
"I", "L", "XXX", "VI", "IV", "XIV", "XXIII-",
"MCM", "MCMXII", "CCXLVI", "DCCLXXXIX", "MMCDXXI", // 1900, 1912, 246, 789, 2421
"CLX", "CCVII", "MIX", "MLXVI" // 160, 207, 1009, 1066
};
int n_samples = sizeof(tests) / sizeof(*tests);
for (int i = 0; i < n_samples; ++i)
{
long number = decimal_from_roman(tests[i], strlen(tests[i]));
printf("%12ld %s\n", number, tests[i]);
}
return 0;
}
int value_of(char ch)
{
switch (ch)
{
case 'I':
return 1;
case 'V':
return 5;
case 'X':
return 10;
case 'L':
return 50;
case 'C':
return 100;
case 'D':
return 500;
case 'M':
return 1000;
default:
return 0;
}
}
Note that the previous code only checks for wrong characters, but doesn't discard strings like "MMMMMMMMMMIIIIIIIIIIIIIV". Consider it just a starting point and feel free to improve it.
Hi, I am still relatively new to CC. May I ask what does the sizeof(tests)/sizeof(*tests) mean? I am guessing that it gets the length of the tests[] array and the * is a pointer. What does the pointer do in this case exactly? That's why in my code, I didn't really use it. But I know it is an important concept to understand for C programming.
@JJ
sizeof(tests)/sizeof(*tests)gets the number of elements in an array.sizeof(tests)provides the size oftestsin bytes.sizeof(*tests)provides the size of the first value (and since they are all the same type, the size of any value) intestsin bytes. If you are compiling to the most recent C++ standards you can use thestd::sizefunction to compute the number of elements with a little less fuss. Note that due to array decay this will not work with an array passed into a function.@JJ I posted a C program, despite your question beeing also tagged as C++, due to the snippet you posted. If you are primarly interested in C++, please edit the question to add that info. Back to your comment, yes, I used that pattern to "automatically" get the size of the array and no, you don't have to use it if you haven't alredy learned how pointers work. I could have explicitly used the size, (e.g.
const char *tests[16] = ...) and then pass that number, but it must be correct (and updated if you decide to add another test) or add a NULL-terminator as a sentinel to stop the loop.