Changing variable's type ... basic

[dean11]

Hi,

this is "elementary my dear watson" stuff, but it beats me.

I use the following:

cout<<"enter a file name\n\n";
    cin>>filenam;
    filename = filenam += ".txt";
    ifstream codedfile( filename.c_str() );  
    if ( codedfile.is_open() )
    {
    codedfile>>sentstring;

to open a file and read it. It's a text file and contains just the string 169abc456fgp
so now
the value of the variable sentstring is 169abc456fgp
- correct?

The following sort of thing:

int une;
une = sentstring[0];
cout<<"first element in sentstring is: "<<une;

should show that une is 1.

But that's not an integer 1, it's a character from a string, so I can't expect that the following:

int deux;
deux= une + 9:

will yield a value of 10.
I must first convert une to type int.

However, if I try it:

int une, deux, trois;
une = sentstring[0];
cout<<"first element in sentstring is: "<<une;
//convert char 1 to int 1
deux=(int) une;
trois=deux + 9;
cout<<"first element in sentstring PLUS 9 = "<<une;

I get 53 or something equally mad.

There must be a simple answer.

In the same vein ...
in the above example, with sentstring being 169abc456fgp
how do I get my code to convert 1 and then 6 and then 9
to integers, but then to realise that the same thing cannot be done with a and b and c, and then to resume converting to integers at 4 and 5 etc etc. ??

Thanks in anticipation

[Tonto]

These are ASCII characters. Look at this table: http://www.lookuptables.com/
You'll see that '1' is 49, and so on. You can just say something along the lines:

int une = sendstring[0] - '0';    // This subtracts the ASCII value of '0' making it "normal"
int deux = une + 9;               // So on and so forth, do what you wish.

You should have the normal numbers that you sought in the first place.
>> how do I get my code to convert 1 and then 6 and then 9 to integers

You can use the isalpha(..) function to check if it a letter, and if it is not then subtract '0' from it like I showed above.

[dean11]

Thanks, that's very helpful.
The sites you referred me to are excellent and I have bookmarked them for later.
However, I still get no joy, because

int une = sentstring[0] - '0';
cout<<"First element in sentstring is "<<une;

is only true if sentstring[0] is 0.

If I try to get smart, as follows:

int middleman;
middleman = sentstring[0];
une=middleman - 'middleman';

which applies your solution regardless of the value of var middleman, I get the error message
multi-character character constant

so obviously it is waiting to convert the type of middleman
to turn it into an ordinary digit.
But how do you do it?!!?

[Tonto]

Can we clarify what you're doing with this?
Do you want to break 169abc456fgp to like

int 129
string abc
int 456
string fgp

? I'm just a bit confused about your intentions

[dean11]

I need to do a lot of operations on the string. This was all easy in Javascript where the processing could be done in a browser but I need a stand-alone exe that will do the same thing.

For a string like
24839971204732176aBIjwOPfdajdsaklfjasQWREUUIORPEQW #
tasks include:
get first element as a digit

in this example where first element is 2,
get next 2 elements as a two digit number

extract the alphabetical part between the numbers and the hatch as a new string

reverse the order of the elements in this new string

and many more:

however, my aim is not just to get this job done, I want to learn the principles.

In Javascript with its weak typing you can just do something like

x = string[0]  // gets first element as a number  e.g. 2
substring=substr(string,1,x) // gets next x elements as an x-long number  e.g. 48

then you'd probably use ereg with regular expressions to identify where the alphabetical part began.
You might use a break statement like

if (string(n)==#){break} // to identify the end of the alphabetical part

and so on.
If Javascript failed to treat a digit as a number you might have to use eval() once in a blue moon.
So, all my problems seem to be with variable type.

[Dweia]

You'd probably find the atoi() function the easiest to use.