ImportantConvert

Question

hiii,
how can i do my project?
string str1="4567995244...4457";
string str2="1458795568...85498";

str1+str2; // addition
str1-str2; // differance
str1*str2; // multiplication
str1/str2; // division

note: we dont use biginteger class  also
we dont use mathematical operators