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;
 }

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);

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)?

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.

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.

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?

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