split string into char array of some size

Question

I an new in c programing so I am not understanding to work for the process.

I have a structure defined like following way.

struct codons
{
    char amino_acid[20], slc[20], dna_codon[40];
};

struct codons c1 = {"Isoleucine", "I", "ATT, ATC, ATA"};
struct codons c2 = {"Leucine", "L", "CTT, CTC, CTA, CTG, TTA, TTG"};

User has to input the string sequence. for example :

printf("Enter the sentence: ");
gets(str);

if user enters string like :

ATTCTGCTTTTA

Then I have to convert this string to 3char length strings like

ATT, CTG, CTT, etc.

and then, I have to check if that this short string of 3 chars present in structure of not.

I dont have any idea how I can convert the string into 3char string length and check.
Can anyone suggest me something?

You need to show how the structure is declared. Showing how it's initialized is not quite the same thing. — unwind
– unwind, Commented Oct 24, 2012 at 12:17
Where's your code so far? At least you're able to get the input from the user and store that right? — Mike
– Mike, Commented Oct 24, 2012 at 12:25

effeffe · Accepted Answer · 2012-10-24 12:32:46Z

4

To get the first 3 characters of a string just allocate a buffer of that size and put there those characters:

char substring[4];
strncpy(substring, input, 3);
char substring[3] = '\0';

Then use strstr to check if a string "possibilities" contains the substring:

if (strstr(possibilities, substring) != NULL)
    // ...

(you didn't posted the struct definition as the comment said, so I can't be more accurate on the real name of "possibilities")

If you want to go on, just do some pointer arithmetic and repeat all the procedure:

strncpy(substring, input + 3, 3)
// and so on...

(lol, I read "condoms")

edited Oct 24, 2012 at 12:32

answered Oct 24, 2012 at 12:18

effeffe

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3 Comments

sam Over a year ago

:P (for condoms)...bdw tx for ur reply. i wll try it nw

codewarrior Over a year ago

I think that you should use 'char substring[4];' and add terminating character at the end (eg substring[3] = '\0';)

effeffe Over a year ago

@codewarrior: yes, I should, thanks. I forgot about strstr and just considered strNcpy. I'm editing.

codewarrior · Accepted Answer · 2012-10-24 15:31:08Z

2

You could do something like below:

char* input_string = ...;

//check if user entered string that could be divided into 3 letters substrings
if (strlen(input_string) % 3 != 0)
  return;

while (*input_string != '\0')
{
   char string_3l[4] = {'\0'};
   strncpy(string_3l, input_string, 3);

   //check if string_3l is part of structure 
   if ((strstr(string_3l, c1.dna_codon) != NULL) || 
               (strstr(string_3l, c2.dna_codon) != NULL))
   {
        //YOU HAVE MATCH!
   }

   input_string += 3;
}

Of course you should check in both c1 and c2 structures.

edited Oct 24, 2012 at 15:31

answered Oct 24, 2012 at 12:31

codewarrior

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1 Comment

codewarrior Over a year ago

Sorry, this was needed in very first version. You can ignore this as this is no longer needed.

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