Why do blank variables display different "weird" results in different computers?

for example:

#include <iostream.h>

int main
{
int a;
double b;
char c;

cout<<a<<"\t"<<b<<"\t"<<c;

return(0);
}

differents values shows up on the screen for a,b and c when the program is run in different computers. Can anyone tell me why this happens? Thanks a bunch.