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Stylo
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 Posted: Thu Sep 10, 2009 10:59 am Post subject: C - annoying question |
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i'v got this question i can't solve...
no matter how hard i think i can't think of a solution
i have to write a program that gets as input a letter (Capital)
and output the forward letter that comes after
and if the input is 'Z' so it should output 'A'
but the catch is i'm not allowed to use conditions
so it suppose to be some ascii code manipulation
please help me lol XD i tried so much time
thanks
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kot1990
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| Posted: Thu Sep 10, 2009 11:38 am Post subject: |
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| Why can't you use conditions? What kind of programming is this? Give an example.
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Flyte
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| Posted: Thu Sep 10, 2009 12:00 pm Post subject: |
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| Code: | char GetNextCapitalChar(char theChar)
{
int f = (int)(theChar - 'A') / ('Z' - 'A');
return f*('A') + (f^1)*theChar + (f^1)*1;
} |
Be sure to put my name in the comments when you hand it in. 
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kot1990
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| Posted: Thu Sep 10, 2009 12:28 pm Post subject: |
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Well I've got a simpler solution by creating a charset with one more letter after Z, so the next will be A again
| Code: | #include <stdio.h>
int main()
{
int i;
char charset[27]; //memory for 27 characters. 26 for A-Z kai one more for the problem of Z.
char letter,enter;
for(i=0;i<=25;i++) //fills the charset with the correct character values.
charset[i] = i + 65;
charset[26] = 65; //the 27th letter will be again A :)
printf("Give a letter: ");
scanf("%c",&letter);
scanf("%c",&enter);
printf("%c",charset[letter-65+1]); //shows the next letter from charset.
getchar();
}
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Stylo
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| Posted: Thu Sep 10, 2009 1:54 pm Post subject: |
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nice way athaem but i forgot to mention that i can't use bitwise operations
i only got + - * / and module (%).
and my guess it should start by using %, correct me if i'm wrong
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kot1990
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| Posted: Thu Sep 10, 2009 2:12 pm Post subject: |
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Great code Athaem 
I was looking to your code about half an hour to understand what it does!
How could you think something like that? just super. I just wanted to say that maybe bitwise operation is still a compare like if but I'm not sure.
I can't think of another code, because the operation is like
output = input + 1;
if it gets to "Z" you will need a condition to check, so output = input + 1; won't work.
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Slugsnack
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| Posted: Thu Sep 10, 2009 3:03 pm Post subject: |
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| Code: | char NextCapital( char GivenChar )
// Precondition : 'A' <= GivenChar <= 'Z'
{
return (char)(((int)(GivenChar + 1 - 'A'))%26 + (int)'A');
} |
you can probably get rid of some of the typecasts/brackets but you get the idea
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kot1990
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| Posted: Thu Sep 10, 2009 3:17 pm Post subject: |
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| Just a single simple line xD. Slugsnack owns!!! , and uses no extra memory and loops like mine.
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&Vage
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| Posted: Thu Sep 10, 2009 3:38 pm Post subject: |
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| I suggest inlining the function.
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Slugsnack
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| Posted: Thu Sep 10, 2009 3:41 pm Post subject: |
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| void:] wrote: | | I suggest inlining the function. |
i'm pretty sure it's for some sort of assignment where he just has to have that function
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Slugsnack
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| Posted: Thu Sep 10, 2009 6:34 pm Post subject: |
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| kot1990 wrote: | Well I've got a simpler solution by creating a charset with one more letter after Z, so the next will be A again
| Code: | #include <stdio.h>
int main()
{
int i;
char charset[27]; //memory for 27 characters. 26 for A-Z kai one more for the problem of Z.
char letter,enter;
for(i=0;i<=25;i++) //fills the charset with the correct character values.
charset[i] = i + 65;
charset[26] = 65; //the 27th letter will be again A :)
printf("Give a letter: ");
scanf("%c",&letter);
scanf("%c",&enter);
printf("%c",charset[letter-65+1]); //shows the next letter from charset.
getchar();
}
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btw, short note. the 65 in your case is of course ascii for 'A'. in programming, numbers such as this, ie. numbers with a significant value, are called magic numbers. magic numbers should not be simply embedded in the code as you have done, it is considered very bad practice. you should either use 'A' instead, which will generate the same code but improve readability or you could use #define like so :
| Code: | | #define FIRSTCAPITAL 65 |
or :
| Code: | | #define FIRSTCAPITAL 'A' |
Last edited by Slugsnack on Sat Sep 12, 2009 4:51 pm; edited 1 time in total |
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FullyAwesome
I post too much
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| Posted: Fri Sep 11, 2009 3:13 am Post subject: |
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this also works:
| Code: | char GetOpposite(char c)
{
return 'Z' - c + 'A';
} |
where logically, you want to get the order the letter is in the alphabet (ie B = 2) by subtracting your letter's ANSCII code from the largest possible, and then add where the letters start in ANSCII code ('A' or 65).
_________________
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Deltron Z
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| Posted: Fri Sep 11, 2009 3:30 am Post subject: |
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Modularity. 
| Code: | | (c + 1 - 'A') % 26 + 'A' |
Work in a modular way, c is the character, get next letter by adding 1 and subtract by 'A' to convert to integer instead ASCII, then use modulo 26 to stay within the range 0~25, since there are 26 letters in the English abc. then simply add 'A' to convert back to ASCII.
For c = 'A' you get 'A' + 1 = 'B' (65 + 1 = 66), subtract 65 and you get 1 (note that 'A' = 0 and 'B' = 1. starting from 0), 1 % 26 = 1, then when you add 'A' you get 'A' + 1 again, which is 'B'.
For c = 'Z' you get 'Z' + 1 = 90 + 1 = 91, subtract 65 and you get 26. 26 % 26 is 0, so you get 'A' + 0 = 'A'.
Edit: Oh, I see slugsnack already showed this way. 
My bad...
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Slugsnack
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| Posted: Fri Sep 11, 2009 5:28 am Post subject: |
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too bad he's not allowed conditions else he could do something like this :
| Code: | char NextCapital( char GivenChar )
// Precondition : 'A' <= GivenChar <= 'Z'
{
return (GivenChar == 'Z'?'A':(GivenChar+1));
} |
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Stylo
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| Posted: Fri Sep 11, 2009 9:52 am Post subject: |
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awesome way Slugsnack really helped me
and thanks for all the others you're awesome too :]
took me few minutes to get the idea of your way Slugsnack
and then i got that with Z entered it'd be 0 value :]
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