Clicker Questions - 05-Bits-Sets
I compile the following program to a.out:
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#include <vector>
#include <iostream>
#include <cstdio>
using namespace std;
int main(int argc, char **argv)
{
vector <string> args;
int x;
int i;
for (i = 1; i < argc; i++) args.push_back(argv[i]);
cin >> hex >> x; // This reads an integer in hex to the variable x
for (i = 0; i < args.size(); i++) {
if (x & (1 << i)) cout << args[i];
}
cout << endl;
return 0;
}
Question 1: What is the output of the following:
UNIX> echo 0x3 | ./a.out a b c d
Answer
It reads3 into x. Only bits 0 and 1 of three are set,
so it prints the first two command line arguments:
UNIX> echo 0x3 | ./a.out a b c d ab UNIX>
Question 2: What is the output of the following:
UNIX> echo 0xc | ./a.out a b c d
Answer
Now it reads0xc into x. Bits 2 and 3 of 0xc are set,
so it prints the last two command line arguments:
UNIX> echo 0xc | ./a.out a b c d cd UNIX>
Question 3: What is the output of the following:
UNIX> echo 0xa5 | ./a.out a b c d e f g h
Answer
Now, the vector is composed of8 strings. We read 0xa5
into x. The bits set in x are bits 0, 2, 5 and 7 (In binary,
x is 1010 0101). So:
UNIX> echo 0xa5 | ./a.out a b c d e f g h acfh UNIX>