CareerCup

int bitcount (unsigned int n) {
int count = 0 ;
while (n) {
count++ ;
n &= (n - 1) ;
}
return count ;
}

int no_of_ones(int n)
{
iny cnt=0;
while(n>0)
{
if(n&1)
cnt++;
n=n>>1;
}
return cnt;
}

It should be a crime to ask this question anymore in interviews.

thanks anny for gave good solution

int countOnes(int x) {
    int count = 0;
    do count += x & 1; while (x >>= 1);
    return count;
}

or:

int countOnes(int x) {
    return (x & 1)
            + ((x & 2) == 2)
            + ((x & 4) == 4)
            + ((x & 8) == 8)
            + ((x & 16) == 16)
            + ((x & 32) == 32)
            + ((x & 64) == 64)
            + ((x & 128) == 128)
            + ((x & 256) == 256)
            + ((x & 512) == 512)
            + ((x & 1024) == 1024)
            + ((x & 2048) == 2048)
            + ((x & 4096) == 4096)
            + ((x & 8192) == 8192)
            + ((x & 16384) == 16384)
            + ((x & 32768) == 32768)
            + ((x & 65536) == 65536)
            + ((x & 131072) == 131072)
            + ((x & 262144) == 262144)
            + ((x & 524288) == 524288)
            + ((x & 1048576) == 1048576)
            + ((x & 2097152) == 2097152)
            + ((x & 4194304) == 4194304)
            + ((x & 8388608) == 8388608)
            + ((x & 16777216) == 16777216)
            + ((x & 33554432) == 33554432)
            + ((x & 67108864) == 67108864)
            + ((x & 134217728) == 134217728)
            + ((x & 268435456) == 268435456)
            + ((x & 536870912) == 536870912)
            + ((x & 1073741824) == 1073741824)
            + ((x & -2147483648) == -2147483648);
}

The logic is to iterate from 1 to 31 and right shift 1 each time. Do an AND with the original number. If the result is non zero then the bit is 1, so increment the count.

int CountOnes (int n)
{
int i,count=0;
for(i=1;i<32;i++)
{ if(n&(1<<i)!=0) count++;
}

cout<< count;

}