Opencv program doesn't work in release mode

Question

I have a program in which i'm trying to see if the image is white or not it works in debug mode but in release it doesn't work

   int image_blanche(char * str, double prctage){
       Mat img=imread(str);
       int compt=0;
       for(int i=0;i<img.rows;i++){
            for(int j=0;j<img.cols;j++){
                if (img.at<uchar>(i,j)==0){
                compt=compt+1;
               }
           }
        }

        if (compt< img.rows*img.cols*prctage)
        {   
            return 1;
        }
       else if (compt> img.rows*img.cols*prctage){
            return 0;
       }
    }