Problem with function!

Why is it evaluating to true? Shouldn't ACGT be skipped?

Quote:

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Code:

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for(x = 0 ; x < strlen(sequence) ; x++)
            {
                while( sequence[x] )
                    {
                        if( sequence[x] == 'U' )
                            {
                                strcpy(out_field, "RNA") ;
                                return ;
                            }
                        else if (sequence[x] != 'A' || sequence[x] != 'C' || sequence[x] != 'G' || sequence[x] != 'T' || sequence[x] != EOF || sequence[x] != '\n' )
                            {
                                strcpy(out_field, "PROTEIN") ; 
                                return ;
                            }
                        else
                            {
                                strcpy(out_field, "DNA" ) ;
                                return ;
                            }
                    }
            }

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When sequence[0] is 'A' on the first time through the loop, this fails:

Code:

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if( sequence[x] == 'U' )

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So then this multi-condition is evaluated:

Code:

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else if (sequence[x] != 'A' || sequence[x] != 'C' || sequence[x] != 'G' || sequence[x] != 'T' || sequence[x] != EOF || sequence[x] != '\n' )

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Is sequence[0] != 'A'? No, (is it equal to 'A'), so this first condition is false, therefore the next condtion is evaluated...

Code:

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if (sequence[x] != 'C' ) ...

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Since sequence[0] is not equal to 'C' (it IS equal to 'A'), then this condition is now true (since you said "OR"), thus, "PROTEIN" is returned.

Todd

Quote:

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Originally Posted by rags_to_riches

You really should learn C before you start messing around with the building blocks of life as we know it...

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You might want to re-evaulate where the fine line between helping someone and doing their homework for them lies.
Posting a totally rewritten solution doesn't help as much as walking someone through it.

Quote:

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Originally Posted by gkoenig

Question: Why couldn't I return the string "DNA" etc directly? Why use "void"?

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You can do that if you make the return type const char*. However, that also means you can't modify your "DNA" string. Otherwise, you would be returning a pointer to a variable that is local to the function. According to scope rules, the local variable would be destroyed when the function returns, thus the function receiving the data would get a pointer to invalid data (garbage).
So to provide a modifiable string, you need to copy it into a proper buffer. And that's why you pass in an argument. But in doing so, there's no need for any return value, thus it's set to void.

Quote:

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Originally Posted by iMalc

You might want to re-evaulate where the fine line between helping someone and doing their homework for them lies.
Posting a totally rewritten solution doesn't help as much as walking someone through it.

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Hmmmm...do you think this is homework? If it is, I totally agree with you. A bioinformatics course maybe? If so, shouldn't the OP have had *some* background in programming before being accepted into such a course?

In any event my totally rewritten solution has been even more totally ignored, so I'm not overly concerned. I could argue that it at least shows the correct logic, which seems to be somewhat of a sticking point here.