循环计数器失败的C ++

Question

Hi I am trying to count the number of zeros after a 1 has occured in a simple 1d array i dont know why the counter is always zero.

int main ()
{
    int testarray[9];
    testarray[0] = 0;
    testarray[1] = 0;
    testarray[2] = 1;
    testarray[3] = 1;
    testarray[4] = 0;
    testarray[5] = 0;
    testarray[6] = 0;
    testarray[7] = 1;
    testarray[8] = 1;

    int counter = 0;
    bool white = false;
    bool prevValue =true;
    bool black = true;
    bool check = false;
    int num = 0;

    for (int i = 0; i<8; i++) {
        num = testarray[i];
        if (num == 1)
            white = true;
        else 
            white = false;


        if((white ==true) && (prevValue == false)) {
            if(i == 0) {
                check = true;
                i++;
            }

            else
                check = false;
        }

        else {
            if (check) 
                counter++;
        }
        prevValue = true;

    }

    cout << "Counter: "<<counter;

    return 0;
}

The practical implementation involves using this for loop to detect edges. I have tried messing with the variables but to no avail. the reason that white =1, and black = 0 is because i am using this loop to solve a vision based problem. Any help would be apreciated.

Answer 1

because prevValue is always true : it never come to this block :

if((white ==true) && (prevValue == false)) {
    if(i == 0) {
    check = true;
    i++;
    }

    else
    check = false;
}

so because of this check is never assigned to 'true' so counter is not incremented

Answer 2

If I have understood all what you need is to find at first 1 and then to count the number of zeroes.

It can be done in one statement if to use standard algorithms.

int counter = std::count( std::find( std::begin( testarray ), std::end( testarray ), 1 ), 
                          std::end( testarray ), 
                          0 );

Answer 3

Because, with this values of the array, check is always false and it need to be true in order to allow counter variable to be incremented as you have written:

 if (check) 
     counter++; 

Also, your for loop doesn't reach the value testarray[8], you've to write

 for (int i = 0; i<9; i++)

in order to include from testarray[0] to testarray[9]