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How to convert string containing numbers (separated by chars) to an int?

This is a discussion on How to convert string containing numbers (separated by chars) to an int? within the C Programming forums, part of the General Programming Boards category; I've read a little bit about atoi() and some similar functions, but I can't get them working to resolve my ...

  1. #1
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    How to convert string containing numbers (separated by chars) to an int?

    I've read a little bit about atoi() and some similar functions, but I can't get them working to resolve my particular problem..

    I've scanned in some numbers in the thousands, and these have a dot "." in them, but I need to be able to treat them as integers.

    Example: my string is "17.334" and I want an int containing just the "17334"

    Thank you in advance for any help provided

  2. #2
    DRK
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    Check each character in the input string. If the character is a digit copy it to a new string. Then use atoi on the new string.
    Adak and kensing like this.

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    I thought your post made enough sense that I would be able to code it, but after moving on and returning to this problem several times, I'm still lost..

    I tried implementing
    Code:
    char new_string_name;
    int int_conversion;
    if(isdigit(data[lineNo].variable)) {
    strcpy (new_string_name, data[lineNo].variable);
    }
    int_conversion = atoi(new_string_name);
    to check characters in the input string, however a few problems arise..

    First of all, I can't figure out how to make my program interpret the array.

    There might well be other problems with the above code that I haven't spotted.. Do I have the parameters right?

  4. #4
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    Since I'm taking these values from an array of strings, I should of course copy and parse them into an array of int's, so it would look more like this:

    Code:
    char new_string[lineNo];
    int int_conversion[lineNo];
    
    for(lineNo = 1; lineNo < MAX_LINES; lineNo++)
    {  
       if(isdigit(data[lineNo].variable))
           {
              strcpy(new_string[lineNo], data[lineNo].variable;
           }
    }
    
    int_conversion[lineNo] = atoi( new_string[lineNo] );
    ..or am I missing/skipping some steps?
    Last edited by kensing; 11-26-2012 at 11:36 AM.

  5. #5
    C++ Witch laserlight's Avatar
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    Your compiler should be giving you some warnings. What are they and what do they mean to you? If you do not get any warnings, then compile at a higher warning level (and if you still don't get any warnings, then you should switch to a more helpful compiler).
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    Look up a C++ Reference and learn How To Ask Questions The Smart Way

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    Actually, yea, loads of warnings.. I should compile more often. I'll start from the beginning I guess, since this whole array subscript thing seems really tricky to me.

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    Quote Originally Posted by kensing View Post
    strcpy(new_string[lineNo], data[lineNo].variable;
    ...
    ..or am I missing/skipping some steps?
    To use DRK's suggestion you need to deal with each character; that means strcpy will not work.

    An alternate suggestion:

    You have a string for example "12.98323" stored in s1 and you want to store the integer in x.
    Code:
    squeeze(s1, ".");
    int x = atoi(s1);
    The function squeeze removes all occurences of "." from s1. This function is defined/suggested as an exercise in Chapter 2 of K&R. Advantages of this "homework" approach:
    1. trying the exercise yourself will give you practice with subscripting
    2. if you can't figure it out you can search online for published solution(s)

  8. #8
    C++ Witch laserlight's Avatar
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    There is yet another possibility: perform the computation to arrive at the integer result yourself, ignoring invalid characters.
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  9. #9
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    Ignoring invalid characters how?

    Another major problem, which is underlying most of my other problems, is how to reference this array that I've built up:

    Code:
    struct kampdata
    {
       char dato[STRENG_LAENGDE_MAX],
              tid[STRENG_LAENGDE_MAX];
            
    };
    typedef struct kampdata kampdata;
    
    kampdata data[LINJER_MAX];
    char linje[LINJE_LAENGDE_MAX];
    int linjeNr = 1;
    FILE *inputfil;
    
    int main()
    {
       inputfil = fopen("superliga-2011-2012.txt", "r");
       if (inputfil != NULL)
       {
          while (linjeNr < LINJER_MAX && fgets(linje, LINJE_LAENGDE_MAX, inputfil) != NULL)
          {
             sscanf(linje, "%s %s\n", data[linjeNr].dato, data[linjeNr].tid);
                 linjeNr++;
          }    
          fclose(inputfil);
        }
    
    printf("%s\n", data[8].dato);
    I got it working, and have no problem printing out all [linjeNr] values of for example data[linjeNr]dato

    But when I want to reference it within a function, for example in regards to this string-to-int-conversion, I'm compiling fine but get no result..

    Edit: apologies if this code was too much off-topic, I'm just a little stressed with this assignment

  10. #10
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    This is what I'm trying to do:

    Code:
    for(linjeNr = 1; linjeNr < LINJER_MAX && (data[linjeNr].hold1score + data[linjeNr].hold2score) >= 5; linjeNr++)
    {
        printf("%s\n", data[linjeNr].tilskuertal);
    }
    ^Compiling fine but nothing is printed

    The code below prints the first value of data[linjeNr].tilskuertal within the inputfile that meets the >=5 requirement, and just keeps spamming that same value instead of continuing to print the next
    Code:
    for(linjeNr = 1; linjeNr < LINJER_MAX; linjeNr++)
    {
      if((data[linjeNr].hold1score) + (data[linjeNr].hold2score) >= 5)
        printf("%s\n", data[linjeNr].tilskuertal);
    }
    Sorry again for any unnecessary confusion caused..

  11. #11
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    I solved the problem with the above code

  12. #12
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    As for the string to int problem, it hit me that I could just scan it as a double instead, multiply by 1000, and then treat them with %.0lf..

    Do you think my teacher might think that this is a bit too much of an imaginative/lazy workaround?

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