It has to be a character array (or converted to one)...
#include <iostream>
int main(int argc, char *argv[]) {
char sys[1024] = "C:\\Program Files\\Internet Explorer\\iexplore.exe ";
char input[256];
std::cout << "What website would you like to view? ";
std::cin >> input;
strcat(sys, input);
system(sys);
return 0;
}