c programming

Question

long fun(char *s) {

long r=0;

for(; *s; r=(r<<1)|(*s++ - '0'));

return r;

}

what does fun("000001010") return??

Answer 1

fun("000001010")  will return decimal value of 000001010 i.e. 10

r is initialised to 0

for(; *s; r=(r<<1)|(*s++ - '0'));

*s is condition checking here and will fail when we will reach end of string 000001010

*s++ will point pointer s to next bit of the string

initially r=0 //r will remain 0 until first bit of input string is 1 so r=0 for string 00000

then r=(0000<<1) OR(1-0)                  //000001

           =0000 OR 0001

          =0001

     

r=(0001<<1) OR(0-0)                        //0000010

           =0010 OR 0000

          =0010

             

r=(0010<<1) OR(1-0)                       //00000101

           =0100 OR 0001

          =0101

 

r=(0101<<1) OR(0-0)                      //000001010

           =1010 OR 0000

          =1010

so r=1010 will be returned whose decimal value is 10