CODEWITHSUNDEEP
c++if-statementboolean
John
John

Reputation: 804

what is the difference between these two c++ code blocks?

Why is the first one able to increment pbf_[k] correctly while the second one does not even do it(increment)for once?

unsigned pbf_[5] ={0}; 
 bool m=0;

Code 1:

for(int k=0;k<5;k++)    
 {

  if((m=(bit_table_[k][i][bit_index ] &bit_mask[bit]))==true)    
     pbf_[k]++;
  }

Code 2:

for(int k=0;k<5;k++)    
 {
   if((bit_table_[k][i][bit_index ] & bit_mask[bit])==true)
        pbf_[k]++;
 }

Upvotes: 5

Views: 214

Answers (4)

Yuk Dara
Yuk Dara

Reputation: 11

I found one problem in your code. You need to use && instead of &. In comparison, && is an logical operator and it differs from &--Bitwise operator.

Example:

if((m=(bit_table_[k][i][bit_index ] && bit_mask[bit]))==true)

To learn about operator in C++ you can visit:http://www.worldbestlearningcenter.com/index_files/c++_operators.htm

Upvotes: 0

Bo Persson
Bo Persson

Reputation: 92261

In the first case, the result of the masking is converted to bool m before it is compared to true.

In the second case, I believe the bitmasks are some integer type. In that case true will be promoted to the same integer type (and have the value 1).

Just remove the == true from the comparison to make them equivalent.

Upvotes: 7

Rohit Srivastava
Rohit Srivastava

Reputation: 278

You first check 

if((m=(bit_table_[k][i][bit_index ] &bit_mask[bit]))==true)

is assining some value to variable m and that is taken by if as true.

Upvotes: 0

Preet Sangha
Preet Sangha

Reputation: 65496

the first on tests the result of the the assignment to m of the value of bit_table_[k][i][bit_index ] & bit_mask[bit], while the second just tests whether

bit_table_[k][i][bit_index ] & bit_mask[bit] results not 0

Both the same effect, except that the first records the result in m on each iteration.

Upvotes: 0

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