Adding binary numbers

Question

Does anyone know how to add 2 binary numbers, entered as binary, in Java?

For example, 1010 + 10 = 1100.

Answer 1

One of the simple ways is as:

1. convert the two strings to char[] array and set carry=0.
2. set the smallest array length in for loop
3. start for loop from the last index and decrement it
4. check 4 conditions(0+0=0, 0+1=1, 1+0=1, 1+1=10(carry=1)) for binary addition for each element in both the arrays and reset the carry accordingly.
5. append the addition in stringbuffer
6. append rest of the elements from max size array to stringbuffer but check consider carry while appending
7. print stringbuffer in reverse order for the answer.

//The java code is as

static String binaryAdd(String a, String b){
    int len = 0;
    int size = 0;
    char[] c1 = a.toCharArray();
    char[] c2 = b.toCharArray();
    char[] max;


    if(c1.length > c2.length){
        len = c2.length;
        size = c1.length;
        max = c1;
    }       
    else
    {
        len = c1.length;
        size = c2.length;
        max = c2;
    }

    StringBuilder sb = new StringBuilder();
    int carry = 0;
    int p = c1.length - 1;
    int q = c2.length - 1;

    for(int i=len-1; i>=0; i--){
        if(c1[p] == '0' && c2[q] == '0'){
            if(carry == 0){
                sb.append(0);
                carry = 0;
            }   
            else{
                sb.append(1);
                carry = 0;
            }   
        }
        if((c1[p] == '0' && c2[q] == '1') || (c1[p] == '1' && c2[q] == '0')){
            if(carry == 0){
                sb.append(1);
                carry = 0;
            }   
            else{
                sb.append(0);
                carry = 1;
            }                   
        }
        if((c1[p] == '1' && c2[q] == '1')){
            if(carry == 0){
                sb.append(0);
                carry = 1;
            }   
            else{
                sb.append(1);
                carry = 1;
            }
        }
        p--;
        q--;
    }

    for(int j = size-len-1; j>=0; j--){
        if(max[j] == '0'){ 
            if(carry == 0){     
                sb.append(0);
                carry = 0;
            }   
            else{
                sb.append(1);
                carry = 0;
            }   
        }
        if(max[j] == '1'){
            if(carry == 0){     
                sb.append(1);
                carry = 0;
            }   
            else{
                sb.append(0);
                carry = 1;
            }   
        }           
    }
    if(carry == 1)
        sb.append(1);   
    return sb.reverse().toString();
}