"1"+"11" = "100"
从右向左相加每一位，从左向右保存在新数组中（注意保存进位，如果存在的情况），然后反转新数组，

char* addBinary(char* a, char* b) {

    int m = strlen(a);
    int n = strlen(b);
    char *array = calloc(m>n?m+2:n+2, sizeof(char));//申请最大的空间m,+1(carry), +1('\0')
    int sum = 0, carry = 0;
    int i = 0;
    array[i++] = 0;//先把'\0' 放在第一个位置，最后会整个翻转
    while(1){
        if(m&&n){// 从后往前相加，反着加
            sum = (a[m-1]-'0'+b[n-1]-'0'+carry)%2;  
            carry = (a[m-1]-'0'+b[n-1]-'0'+carry)/2;
            m--;
            n--;
        }else if(m){
            sum = (a[m-1]-'0'+carry)%2;  
            carry = (a[m-1]-'0'+carry)/2;
            m--;

        }else if(n){
            sum = (b[n-1]-'0'+carry)%2; 
            carry = (b[n-1]-'0'+carry)/2;
            n--;

        }else
            break;
        array[i++] = sum+'0';//每次保存下来当前位的相加和（不算进位carry）
    }
    if(carry)
        array[i++] = '1';
    int left = 0;
    int right = i-1;    //反转整个字符串
    while(left < right){
        char tmp = array[left];
        array[left] = array[right];
        array[right] = tmp;
        left++;
        right--;
    }   

    return array;
    
}