How to create a code which identifies whether the user input is composed of the only characters specified in the program?

Question

Like for example,
the code dictates that the input value (a string) can only have characters +,-,*,/,% and 1,2....,9 in this sequence only, if the user input is not of this form, then the code will not run.
input - ace..did
outputs an error.

input - %4
runs the code.

Answer 1

You can use a code like this

std::string input;
cin >> input;
std::string in = input;

if(in.find('+') != in.npos) in.erase(std::remove(in.begin(), in.end(), '+'), in.end());
//do this for all the characters you want in string

if(in.empty) runcode
else
don't run code

you didn't say what language you want I wrote in c++ but you can convert this code into any other language