the code needs to execute something depending on the .png filename passed as argv[1].
C++ switch does not accept strings, so all the files are named as cN.png where N is a digit between 0 and 9 and this digit is accessed with
string a=argv[1];
char aa=a[1];
On filename c6.png line
cout<<"aa="<<a[1]<<"; isdigit(aa)="<<isdigit(aa)<<endl;
returns aa=6; isdigit(aa)=1
yet switch(aa) seems to convert value 6 into its ASCII decimal code 54
I can get round it by replacing case 6 with case 54 in swich. Yet keen to know how to use swich in a more direct way. Perhaps aa should be of a different type?