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anonymous

  • 5 years ago

C Question: What's wrong with my program? [2]

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  1. anonymous
    • 5 years ago
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    This is supposed to be a program that accepts an integer from 1 to 3,999 and converts it to Roman numeral form. Initially the values for the digits I got were correct, but when I added the switch sections of the code I get decimal numbers for the digits. Also, the switches themselves don't seem to be working well as the program can only choose between case 1 and default. I suspect that the error has something to do with how I dealt with the strings. #include <stdio.h> int main (void) { int Num, Digit[4]; char *RThou[5], *RHund[5], *RTens[5], *ROnes[5]; // Digit[3]: Thousands digit | RThou[5]: Thousands digit in Roman numerals // Digit[2]: Hundreds digit | RHund[5]: Hundreds digit in Roman numerals // Digit[1]: Tens digit | RTens[5]: Tens digit in Roman numerals // Digit[0]: Ones digit | ROnes[5]: Ones digit in Roman numerals printf("Input an integer from 1 to 3,999: "); scanf("%d", &Num); if (Num < 1 || Num > 3999) printf("Invalid input.\n"); else { Digit[3] = Num/1000 % 10; Digit[2] = Num/100 % 10; Digit[1] = Num/10 % 10; Digit[0] = Num % 10; switch (Digit[3]) { case 1: RThou[5] = "M"; printf("M"); break; case 2: RThou[5] = "MM"; printf("MM"); break; case 3: RThou[5] = "MMM"; printf("MMM"); break; default: RThou[5] = ""; break; } switch (Digit[2]) { case 1: RHund[5] = "C"; break; case 2: RHund[5] = "CC"; break; case 3: RHund[5] = "CCC"; break; case 4: RHund[5] = "CD"; break; case 5: RHund[5] = "D"; break; case 6: RHund[5] = "DC"; break; case 7: RHund[5] = "DCC"; break; case 8: RHund[5] = "DCCC"; break; case 9: RHund[5] = "CM"; break; default: RHund[5] = ""; break; } switch (Digit[1]) { case 1: RTens[5] = "X"; break; case 2: RTens[5] = "XX"; break; case 3: RTens[5] = "XXX"; break; case 4: RTens[5] = "XL"; break; case 5: RTens[5] = "L"; break; case 6: RTens[5] = "LX"; break; case 7: RTens[5] = "LXX"; break; case 8: RTens[5] = "LXXX"; break; case 9: RTens[5] = "XC"; break; default: RTens[5] = ""; break; } switch (Digit[0]) { case 1: ROnes[5] = "I"; break; case 2: ROnes[5] = "II"; break; case 3: ROnes[5] = "III"; break; case 4: ROnes[5] = "IV"; break; case 5: ROnes[5] = "V"; break; case 6: ROnes[5] = "VI"; break; case 7: ROnes[5] = "VII"; break; case 8: ROnes[5] = "VIII"; break; case 9: ROnes[5] = "IX"; break; default: ROnes[5] = ""; break; } printf("%d %d %d %d\n", Digit[3], Digit[2], Digit[1], Digit[0]); printf("%c %c %c %c\n", *RThou[5], *RHund[5], *RTens[5], *ROnes[5]); } }

  2. anonymous
    • 5 years ago
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    I don't know C but problem is NOT with switch statements printf("%c %c %c %c\n", *RThou[5], *RHund[5], *RTens[5], *ROnes[5]); maybe this prints ONLY 1 character?

  3. anonymous
    • 5 years ago
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    You're accessing memory that's out of the boundaries of your array in ALL of your switch() statements. For example, you are writing RThou[5] even though RThou[] is a char* array of size 5; arrays in C (and other languages like C++, Java, Python, etc) are zero-indexed, which means you can only subscript an array from 0 to array_size-1: i.e. if I declare an array A[10], I can only use A[0], A[1], ..., A[9] and anything else would be undefined behavior.

  4. anonymous
    • 5 years ago
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    that's what i thought, because always 1 char was written

  5. anonymous
    • 5 years ago
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    but in others languages i would use String for it :P

  6. anonymous
    • 5 years ago
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    in C, you could make good use of <string.h> here

  7. anonymous
    • 5 years ago
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    @Tomas.A: Yep, I realized soon enough that changing %c to %s should allow me to print more than 1 character. @agdgdgdgwngo: I'm afraid I'm not sure if I understand you. So if we imagine RThou[5] to look like this: [] [] [] [] [] 0 1 2 3 4 Does it mean in my switch statements, I'm trying to jam all those characters in a slot that does not exist? How can I make them fit into slots 0-4?

  8. anonymous
    • 5 years ago
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    right. try dereferencing valid slots.

  9. anonymous
    • 5 years ago
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    But if that's the case, how come it works for the first 2 digits, and fails for the last 2?

  10. anonymous
    • 5 years ago
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    switch (Digit[3]) { case 1: RThou[5] = "M"; printf("M"); break; case 2: RThou[5] = "MM"; printf("MM"); break; case 3: RThou[5] = "MMM"; printf("MMM"); break; default: RThou[5] = ""; break; } you are using printf statements there.

  11. anonymous
    • 5 years ago
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    Even without the printf statements, the program is able to identify the correct values for the thousands and hundreds digits. Just not the tens and ones digits.

  12. anonymous
    • 5 years ago
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    Okay, it seems that changing Digit[0] to Digit[4] makes the program output the correct value for the ones digit.

  13. anonymous
    • 5 years ago
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    digit[4] doesn't give you a segfault?

  14. anonymous
    • 5 years ago
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    For some weird reason, no.

  15. anonymous
    • 5 years ago
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    post the code on a site like http://ideone.com so we can debug it

  16. anonymous
    • 5 years ago
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    Here: http://ideone.com/nK1OV

  17. anonymous
    • 5 years ago
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    http://ideone.com/vaYtT works alright O.o

  18. anonymous
    • 5 years ago
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    Ah. The tens digit will always output to 1. '3333' should not work.

  19. anonymous
    • 5 years ago
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    http://ideone.com/2L3MA got rid of all the out of array bounds stuff

  20. anonymous
    • 5 years ago
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    Hmm. Never knew you could just do away with declaring the number of slots in a string. Does that work for arrays of other data types?

  21. anonymous
    • 5 years ago
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    I don't think so :(

  22. anonymous
    • 5 years ago
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    If I *really* wanted to specify the number of slots in the strings, what should I have done?

  23. anonymous
    • 5 years ago
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    you can do lots of stuff, like defining char arrays of specific sizes, malloc(), etc.

  24. anonymous
    • 5 years ago
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    Another question: How come removing the array bounds made the code work?

  25. anonymous
    • 5 years ago
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    It actually works even when you are storing your strings in places outside the bounds of your arrays, since you are operating on the stack.

  26. rsmith6559
    • 5 years ago
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    Since you declared the thousands, hundreds, tens and ones consecutively, when you were going beyond the end of the thousands you could possibly have been putting the thousands value into the hundreds, then the hundreds values into the tens, and sooner or later putting the value into who knows what.

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