Question

i want to extract number string values of a char array. Actually I want to extract numbers embeded in file names for some file management. For example if there is a file name as file21 then i want the decimal number 21 from this file name.

How can i extract these values?

I tried the following but it results in an unexpected value. I think it is as a result of the implicit typecasting from the char to int while doing the arthimetic operation.

char * fname;
cout<<"enter file name";
cin>>fname;

int filenum=fname[4]%10+fname[5];
cout<<"file number is"<<filenum;

NOTE:
The filenamse are strictly in the format fileXX, XX being numbers between 01 and 99

Answer 1

You need to subtract '0' to get the decimal value of a digit character:

int filenum=(fname[4]-'0')*10+(fname[5]-'0');

Better yet, you should use atoi:

int filenum = atoi(fname+4);