Thread: It works but, there's confusion, please help with this solution.

Hey Guys,

My code works as it is supposed to according to the problem in the book. I wish I could say that I learned a lot as it took me several hours to complete. The truth is, I hacked my way through it by trying this and that until it worked. Terrible I know.

Code:

//http://knking.com/books/c2/answers/c13.html
#include <stdio.h>

int main(){
    char *digOne[]={"twenty", "thirty", "fourty", "fifty", "sixty", "seventy", "eighty", "ninety"};
    char *digTwo[]={"zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine", \
"ten", "eleven", "twelve", "thirteen", "fourteen", "fifteen", "sixteen", "seventeen", "eighteen", "nineteen"};
    char num[9];
    int x;
    printf("Enter a two-digit number: ");
    scanf("%s", num);                     // I enter 23 - it is saved as a string in num


    if(num[0]=='0'){                        //'0' could be changed 48
        sscanf(num, "%d", &x);              // saves num as an int inside x
        printf("%s", digTwo[x]);            // works marvelously
    }
    else if(num[0]=='1'){                   //'1' could also be 49
        sscanf(num, "%d", &x);              // same as above
        printf("%s", digTwo[x]);            // works marvelously
    }
    else{
        char both[5];
        char ones, tens;
        sscanf(num, "%s", both);            // this time saves num as a string placed in both
        tens = both[0];
        printf("tens as int: %d\n", tens);  // 2 prints as 50
        printf("tens as char: %c\n", tens); // 2 prints as 2 but, I think it is '2' 
        ones = both[1];
        printf("%s", digOne[tens-'2']);     //'2' could also be 50
        if(digTwo[ones-48]!="zero"){
            printf(" %s", digTwo[ones-'0']); //'0' could also be 48
        }
    }


    return 0;
}

I understand why it all works but, I'm sure there was a much cleaner way to solve this problem and the answer to the problem is not provided in the book. I think it is inefficient how I converted things from integer to string, etc. I'm sure there is a better way.

Is anyone willing to show me a simpler way to make it work? This is an area of c programming that I really struggle with (I.e. converting strings to integers and vice versa). Thank you for any comments.

I would get the input as an integer,

Then if less then zero, error out
If more than 99, error out.

If less than 20 print digTwo(number)

Otherwise print digOne (number divided by 10 subtract 2) followed by digTwo (number mod 10)

Here's one thing that is doing unnecessary work:

Originally Posted by mpatters

Code:

        char both[5];
        char ones, tens;
        sscanf(num, "%s", both);            // this time saves num as a string placed in both

num is already a string read in by scanf, so this sscanf does nothing but copy num to both. You don't modify num or both in the following code, so why not just use num where you use both?

Code:

    else{
        char ones, tens;
        tens = num[0];
        printf("tens as int: %d\n", tens);  // 2 prints as 50
        printf("tens as char: %c\n", tens); // 2 prints as 2 but, I think it is '2' 
        ones = num[1];
        printf("%s", digOne[tens-'2']);     //'2' could also be 50
        if(digTwo[ones-48]!="zero"){
            printf(" %s", digTwo[ones-'0']); //'0' could also be 48
        }
    }

But I wouldn't even bother with that change; I'd start with getting a number as an int directly:

Code:

int num;
scanf("%d", &num);

And then do arithmetic/tests on the integer rather than mess around with looking at the digits:

Code:

if (num < 20) {
  printf("%s\n", digTwo[num]);
} else if (num < 100) {
  int tens = num / 10;
  int ones = num % 10;
  if (ones != 0) {
    printf("%s %s\n", digOne[tens], digTwo[ones]);
  } else {
    printf("%s\n", digOne[tens]);
  }
}

Untested.

Also note that

Code:

if(digTwo[ones-48]!="zero")

produces Undefined Behavior, you can't compare two strings like that, you would need to use strcmp().

Thanks hamster_nz and christop, that code you gave me is so much easier to follow than the maze that I coded. Using \10 and %10 is something that should have come into my mind but, didn't.... Great job guys. Awesome. Onto the next exercise...

Originally Posted by jimblumberg

Also note that

Code:

if(digTwo[ones-48]!="zero")

produces Undefined Behavior, you can't compare two strings like that, you would need to use strcmp().

Is it undefined behavior or only implementation defined? AFAIK it's perfectly legal to compare two pointers, but the result won't necessarily be what you want or expect because some implementations merge identical string literals (the pointers will be equal) while some don't (the pointers won't be equal).