I used "to" keyword which "std.conv" includes for data conversions, but I think that there are some other ways for data conversions, or maybe there are common ways like casting, I hope to know about. For example, next program are using "to":
// D programming language
import std.stdio;
import std.conv;
import std.string;
int main()
{
char[] s;
int x=0, e;
do{
try{
e=1;
write("Enter a numeric value: ");
readln(s);
s=strip(s);
x=to!int(s);}
catch (Exception err){
stderr.writefln!"Warning! %s"(err.msg);
e=0;}
}while(!e);
writeln("Correct numeric value!");
return 0;
}