#include <iostream>
#include <string>
#include <regex>
using namespace std;
int main() {
string userInput = "=";
regex infix(R"([()\d+/*-]+)");
if(regex_match(userInput,infix)){
cout<<"Valid expression!\n";
} else {
cout<<"Error: Not a valid infix expression!\n";
}
return 0;
}
I2luY2x1ZGUgPGlvc3RyZWFtPgojaW5jbHVkZSA8c3RyaW5nPgojaW5jbHVkZSA8cmVnZXg+CnVzaW5nIG5hbWVzcGFjZSBzdGQ7CgppbnQgbWFpbigpIHsKCXN0cmluZyB1c2VySW5wdXQgPSAiPSI7CglyZWdleCBpbmZpeChSIihbKClcZCsvKi1dKykiKTsKCWlmKHJlZ2V4X21hdGNoKHVzZXJJbnB1dCxpbmZpeCkpewoJICAgIGNvdXQ8PCJWYWxpZCBleHByZXNzaW9uIVxuIjsKCX0gZWxzZSB7CgkJY291dDw8IkVycm9yOiBOb3QgYSB2YWxpZCBpbmZpeCBleHByZXNzaW9uIVxuIjsKCX0KCXJldHVybiAwOwp9