I just finished a program EXACTLY like yours. The system() command cannot take a 'string' variable. This is how you do it though. Here's an example of what to do:
Code:
#include <iostream.h>
#include <cstring>
char first[] = "net send ";
char msg[50];
char final[200];
char comp[50];
cout<<"Enter a message: "<<flush;
cin>>msg;
cout<<endl<<"Enter the computer name: "<<flush;
cin>>comp;
strcpy(final, first);
strcat(final, comp);
strcat(final, " "); //puts in a space
strcat(final, msg);
system(final);