Need function to convert bool array to int- why doesnt this work?

Question

Hey I wrote this function to convert an bool array to int: (Math Lob included):

bool b_array[5];
int convertToInt(start_index,stop_index){
 int run=0;
 int result=0;
 for(int id=start_index;id<=stop_index;id++){
 result+=b_array[id] * pow(2.0,run);
 run++;
 }
 return result;
} 

but it doesnt this work?

Thanks and kind regards Nic

• chrisl: "Does not work" is a poor problem description. Explain what it actually does and what you expected it to do. Provide a minimal but complete test sketch, that shows the problem
• Maximilian Gerhardt: You seem to want to convert an array of bools into the respective integer value, so e.g. { false, true, true, false} into 0b0110 = 6? Then you should use better casting, so (int)b_array[id] and (int)pow(2.0,run). Though it's a weird way to do it, since bitshifting would be more appropriate (result += b_array[id] ? (1 << run) : 0) . Also be aware of the numerical limits of your 16-bit signed int.
• Delta_G: The pow function returns a float. Floats are inherently inaccurate. The index to the array has to be an int. When you do powers of 2 with pow you don’t actually get 4. You get 3.9999999 something. So when that gets truncated it turns into 3 and not the 4 that you want. Use bit shifting for integer powers of 2 and you won’t have this problem.
• Nic: Thank you Guys a lot! It worked like a charm but I could not have made it without you!

Answer 1

Assuming little-endian bools (least significant bool first), you should use simple bit-shifting, not floating point power calculations:

for(int id=start_index;id<=stop_index;id++){
 result |= b_array[id] ? (1 << run) : 0;
 run++;
}

The ternary operation (b_array[id] ? (1 << run) : 0) means:

• If b_array[id] is true, then
  • Or result with 1 left-shifted run times and store in result
• otherwise
  • Or result with 0 and store the result (no-operation).

• KIIV: You can simplify this in C++ because bool value promoted to an integer is 0 or 1. So (b_array[id] << run) can be used. In C there is no bool data type, so something like ((b_array[id] !=0) << run) should be used. And i like for example result = (result<<1) | b_array[id]; more (it can be result = result*2 + b_array[id] too)
• Nic: Thank you for your Solution and your explaination, it worked on first try like a charm! Thank you a lot, I could not have solved that without your help!