simple char array question..

This is a discussion on simple char array question.. within the C++ Programming forums, part of the General Programming Boards category; Hey all, I'm trying to use strcat with input as follows: Code: strcat(top, input[y]); // where y is a loop ...

  1. #1
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    simple char array question..

    Hey all,

    I'm trying to use strcat with input as follows:

    Code:
    strcat(top, input[y]); // where y is a loop var
    top is declared as

    char top[256] = ""; // but is later filled

    and input is

    char input[256];


    (these aren't my actual variable names, however).

    Unfortunately my compiler says "Invalid conversion from 'char' to 'const char*'" (gcc in KDevelop)


    What should I do?

    Here is all of the code just in case (a work in progress!):

    Code:
     #include <iostream>
     #include <cstring>
     
     using namespace std;
    
     int main()
     {
     
        char input[256];
        char top[256] = "";
        float ftop;
        char bottom[256] = "";
        float fbottom;
        int input_length;
        bool divide = false;
        float answer;
        char *pointer;
        char *pointer2;
    
        cout << "This program adds, subtracts, multiplies and divides fractions.";
        cout << endl << "(or it will when I'm done)" << endl;
        cout << "Enter a fractional number: (i.e. 5/2)" << endl;
        cin.get(input, 256);
        input_length = strlen(input);
    
        for(int x = 0; x < input_length; x++)
        {
          if(input[x] > 48 && input[x] < 57)
          {
            for(int y = x; input[y] > 48 && input[y] < 57; y++) // take in all numerical digits
            {
              if(divide == false)
              {
                
                pointer2 = &input[y];
                strcat(top, input[y]); // puts it in top of / hasn't been encountered
              }
              if(divide == true)
              {
                
                pointer2 = &input[y];
                strcat(bottom, input[y]); // puts them in bottom if it has
              }
            }
          }
          if(input[x] == '/') divide = true;
          if(input[x] == '\0');
          else cout << "Invalid input.";
        }
    
        ftop = atoi(top);
        fbottom = atoi(bottom);
    
        answer = ftop/fbottom;
    
        cout << answer;
    
        return 0;
     }

  2. #2
    Guest Sebastiani's Avatar
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    Waterloo, Texas
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    strcat will append a char array to a char array. Try:


    Code:
    char beta[2];
    beta[1] = '\0';
    
    
    do{
    
    beta[0] = input[i];
    strcat(alpha, beta);
    
    }while(1);



    ITSA
    Socket Library!

  3. #3
    Banned master5001's Avatar
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    Sebastiani's code may be correct. But I didn't read all of your code. I just read the part you said that was giving you the error:

    Code:
            for(int y = x; input[y] > 48 && input[y] < 57; y++) // take in all numerical digits
            {
              if(divide == false)
              {
                
                pointer2 = &input[y];
                strcat(top, input[y]); // puts it in top of / hasn't been encountered
              }
              if(divide == true)
              {
                
                pointer2 = &input[y];
                strcat(bottom, input[y]); // puts them in bottom if it has
              }
            }
    How about changing strcat(top, input[y])--note that you are passing a char in the second parameter which is causing the error--to strcat(top, pointer2)?

  4. #4
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    Originally posted by master5001
    Sebastiani's code may be correct. But I didn't read all of your code. I just read the part you said that was giving you the error:

    Code:
            for(int y = x; input[y] > 48 && input[y] < 57; y++) // take in all numerical digits
            {
              if(divide == false)
              {
                
                pointer2 = &input[y];
                strcat(top, input[y]); // puts it in top of / hasn't been encountered
              }
              if(divide == true)
              {
                
                pointer2 = &input[y];
                strcat(bottom, input[y]); // puts them in bottom if it has
              }
            }
    How about changing strcat(top, input[y])--note that you are passing a char in the second parameter which is causing the error--to strcat(top, pointer2)?
    Hmm I feel quite stupid. I put in the pointer and then didn't even change the strcat... plus I realized that even with that code, it will only append one char at a time. I can fix that though.

    Anyways, now it always says "invalid input"...

    here's the output -

    Code:
    This program adds, subtracts, multiplies and divides fractions.
    (or it will when I'm done)
    Enter a fractional number: (i.e. 5/2)
    5/2
    Invalid input.Invalid input.Invalid input.0
    Press Enter to continue!
    Any tips? Thanks.
    Last edited by Captain Penguin; 10-14-2002 at 05:05 PM.

  5. #5
    Registered User
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    1,595
    in your code you have three if statements and a single else. The else only relates to the last if statement. So if the input[i] isn't a NULL char the else statement will output the invalid input statement. You should use one if, 2 else if's, and a single else.

  6. #6
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    Hmm makes sense. I always skipped over the sections in my book explaining if's since I thought I knew them already

    Anyways, now the "answer" is always "nan". What the hell does that mean?

  7. #7
    btq
    btq is offline
    julie lexx... btq's Avatar
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    haven't really followed this thread but I still can contribute:
    NaN stands for 'not a number'..
    urhh..had some nice links for it but they seem to have dissapeared..

    /btq
    ...viewlexx - julie lexx

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