CSC231 Powers of 2 in C++

--D. Thiebaut 13:43, 8 October 2010 (UTC)

---

This exercise is a companion of the same exercise dealing with a Python implementation of the program.

Exercise

• Below is a C++ program, and its complete output

Question 1

Do the numbers output by the program look correct?

Question 2

Remove the comment sign (//) in front of the last printf. Compile and run the program again.

Explain the new output!

Question 3

Remove the word unsigned from the program. This changes the integer variable from an unsigned variable to a signed one.

Change the %u printing format command by %d to indicate that you want to print the contents of a signed variable.

• Predict the output of the program.
• Verify whether you were correct in your prediction!

The C++ Program

// mulby2.cpp
// D. Thiebaut
// To compile and run:
// 
//   g++ -o mulby2 mulby2.cpp
//   ./mulby2
//
#include <stdio.h>

int main() {
  unsigned int x = 1;

    for ( int i=0; i<32; i++ ) {
       printf ( "%u\n", x );
       x = x * 2;
    }

  //printf( "final x = %u\n\n", x );
  return 0;
}

The Output

g++  -o  mulby2  mulby2.cpp

./mulby2 

1
2
4
8
16
32
64
128
256
512
1024
2048
4096
8192
16384
32768
65536
131072
262144
524288
1048576
2097152
4194304
8388608
16777216
33554432
67108864
134217728
268435456
536870912
1073741824
2147483648