Help with roman numeral calculator

[arkine]

So I am trying to write a program that converts roman numerals into decimal numbers.

I so far have come up with:

#include <stdio.h>
#include <ctype.h> // importing the tolowerfunction
//variables
int decimal, total;
char numeral[];






//prototypes
int decimal_to_roman(char input);
int roman_to_decimal(char letter);




int roman_str_to_decimal(char input)
{
    int i;


    for (i=0; i< strlen(input); i++)
    {
         total += roman_to_decimal(numeral[i]);




    }


}


int roman_to_decimal(char letter)
{
    switch(tolower(letter))
    {
        case 'm':
            return 1000;
        case 'd':
            return 500;
        case 'c':
            return 100;
        case 'l':
            return 50;
        case 'x':
            return 10;
        case 'v':
            return 5;
        case 'i':
            return 1;
        default:
            break;
    }
}




int main(void)


{






printf("Please enter the first number: ");
scanf("%s", &numeral);


roman_str_to_decimal(numeral);


printf("%d\n", total);




//printf("%c\n", numeral[2]);




}

but each time I compile it, it times out as if it were hitting an infinite loop. I have a feeling that I am not passing an individual character to the roman_to_decimal function but am unsure why.

[grumpy]

1) The declaration "char numeral[]" does not specify a string of arbitrary length, but your main() function treats it as if it is in the scanf() call.

2) strlen() is specified in <string.h>, and you have not #include'd that header file.

3) roman_str_to_decimal() is treating a single char as if it was an array of char. It is not.

4) You need to compile with maximum warnings. In other words, get your compiler to issue as many diagnostics as possible. Your compile would have picked up most the problems above.

5) Roman values do not work only left to right. IX is the value 9. XI is the value 11. Your code will not recognise the difference between them.

[arkine]

1) The declaration "char numeral[]" does not specify a string of arbitrary length, but your main() function treats it as if it is in the scanf() call.

2) strlen() is specified in <string.h>, and you have not #include'd that header file.

3) roman_str_to_decimal() is treating a single char as if it was an array of char. It is not.

4) You need to compile with maximum warnings. In other words, get your compiler to issue as many diagnostics as possible. Your compile would have picked up most the problems above.

5) Roman values do not work only left to right. IX is the value 9. XI is the value 11. Your code will not recognise the difference between them.

Thanks for the reply.

In this example, I am trying to pass it a string such as MXII and not a single char and then have the roman_str_to_decimal() take the nth index of the input and send it through the other function to generate the value for total.

I am just having problems sending an individual letter to my switch statement.

[arkine]

#include <stdio.h>
#include <ctype.h> // importing the tolowerfunction
#include <string.h>// for the strlen()
//variables
int decimal, total;
char numeral[10];






//prototypes
int decimal_to_roman(char input);
int roman_to_decimal(char letter);
int roman_str_to_decimal(int input);




int roman_str_to_decimal(int input)
{
    int i;


    for (i=0; i< strlen(input); i++)
    {
       total += roman_to_decimal(numeral[i]);




    }


}


int roman_to_decimal(char letter)
{
    switch(tolower(letter))
    {
        case 'm':
            return 1000;
        case 'd':
            return 500;
        case 'c':
            return 100;
        case 'l':
            return 50;
        case 'x':
            return 10;
        case 'v':
            return 5;
        case 'i':
            return 1;
        default:
            break;
    }
}




int main(void)


{






printf("Please enter the first number: ");
scanf("%s", &numeral);


roman_str_to_decimal(numeral);


printf("%d\n", total);




printf("%c\n", numeral[2]);




}

ok never mind, forgot to prototype and enter the correct datatype for one of my functions. It now spits out the correct number. Thank you for the help.

[anduril462]

Read up on arrays, it seems you're missing a few basics. Textbooks, Google for tutorials, etc.

Declare numeral to have a size, so there is actually room in it for your string:

#define MAX_NUMERALS  10  // constants allow you to easily change the size by changing just one line

int main(void)
{
    int decimal_value;
    char numeral[MAX_NUMERALS + 1];  // +1 for the null terminator that marks the end of a string in C

    decimal_value = roman_str_to_decimal(numeral[2]);  // pass the 3rd char in numeral to the function

Remember, in C, valid array indexes are from 0 to SIZE-1. That's why numeral[2] is actually the 3rd char (numeral[0], numeral[1], numeral[2]).

[SirPrattlepod]

ok never mind, forgot to prototype and enter the correct datatype for one of my functions. It now spits out the correct number. Thank you for the help.

If it spits out the correct number I would say it's a matter of chance and somewhat like a game of Russian Roulette

For example:

Given

int input;

What do you expect

strlen(input)

to return?