C Array Count (Beginner) [duplicate]

Answer 1

c-'0' is technique to give int value == to char number e.g. 1 for '1' , 5 for '5'.

char symbols '0', '1', '2' ..... '9' are assigned continue encoding values so difference of a numeric char constant with '0' gives decimal number. (in your compiler for example in ASCII char they are assigned continues acsii values).

So for example in variable c is '7', then c - '0' == 7;

In your code array declared as:

int ndigit[10]= {0};   
                // default initialized with `0`

So index can be from 0 to 9. So in you code:

++ndigit[c-'0'];  // ndigit[c-'0'] = ndigit[c-'0'] + 1;

increments frequency of a number by 1 when at corresponding digit of a number char.

Answer 2

((c = getchar()) != EOF)
        if (c >= '0' && c <= '9')
            ++ndigit[c-'0'];

c gives you the current character. With the range checking you confirm it is a number by using its ASCII value _{Check chr column for 0, it says 48 and for 8 it says 56.So, '8'- '0' gives 56 - 48 = 8}

ndigit is used to keep track of how many times a number occurs in with each element of the array representing the number of times its subscript has occured. ndigit[0] will ggive you number of times 0 has occurred and so on.. ndigit[x] gives number of times x appeared

[c - '0']

suppose your c i.e current character is 8 then '8' - '0' will give you 8. so you get ndigit[8] and you ++ that value [you initialised it to 0 at start]