C Programming

Question

long fun( char * s){
    long r = 0;
    for( ; *s ; r = (r << 1) | (*s++ - '0'));
    return r;
}

What does the fun("000001010") returns?

Answer 1

(*s++ - '0') this will subtract ascii value of stored character with ascii value of 0 and will give numeric (decimal ) value of stored character during each iteration,

example: ascii value of 0 and 1 is 48 and 49 , hence during iteration 1:

(*s++ - '0')=s[0]-'0'='0'-'0'=48-48=0(decimal value)

now evaluation of ur program is as given below : fun("000001010")

iteration	r<<1	(*s++-'0')=value stored at s[i]	r = r<<1|(*s++ - '0')
1	0	0	0
2	0	0	0
3	0	0	0
4	0	0	0
5	0	0	0
6	0	1	1
7	2	0	2
8	4	1	5
9	10	0	10
10		\n(ascii value 0)	loop fail

therefore 10 will be return at the end

Answer 2

r   s

0  0                                                                                                                                                                            

0  0                                                                                                                                                                            

0  0                                                                                                                                                                            

0  0                                                                                                                                                                            

0  0                                                                                                                                                                            

0  1                                                                                                                                                                            

1  0                                                                                                                                                                            

2  1                                                                                                                                                                            

5  0     

at last r = r*2 = 10

 

return value will be 10

Comments

Not clear, can you please elaborate a bit more please