array concepts need

**Shinzu911** · 05-04-2012

can someone please explain this to me ?

Code:

if (c >= '0' && c <= '9')
++ndigit[c-'0'];  // this line > what is it and what does it do?

taken from K&R:

Code:

 
#include <stdio.h>
int main(void)
{
    int c, i, nwhite, nother;
    int ndigit[10];
    nwhite = nother = 0;
    
    for (i = 0; i < 10; ++i)
    ndigit[i] = 0;
    while ((c = getchar()) != EOF)
         if (c >= '0' && c <= '9')
              ++ndigit[c-'0'];
         else if (c == ' ' || c == '\n' || c == '\t')
              ++nwhite;
         else
              ++nother;
         printf("digits =");
         for (i = 0; i < 10; ++i)
              printf(" %d", ndigit[i]);
         printf(", white space = %d, other = %d\n",nwhite, nother);
return 0;
}

any help is appreciated thank u

**stahta01** · 05-04-2012

Code:

++ndigit[c-'0'];

c is an integer variable representing, the result of getchar (a ASCII character in most cases). And, in this case it represents an ASCII digit between '0' and '9'.

When the value of the ASCII code for '0' is subtracted from it.
The answer yields an integer between 0 and 9.

The rest of the meaning of the line should be clear if you understand integer arrays and the ++ operator.
I am not sure how to explain arrays; I learned them so long ago; I just can not remember ever not know the meaning.

Maybe, this link will help you.
Arrays in C - Cprogramming.com

Things to remember on C arrays the first element is always numbered 0.
The last legal index value is always one less that declared. In this case the max legal index is 9.

Code:

int ndigit[10];

The above line declares an array called ndigit with the size of 10.
The first element index is 0 the last element index is 9.

Tim S.

**Shinzu911** · 05-04-2012

i'm ok with arrays it was the part above which u answered i didn't understand thank you that helps allot

**Salem** · 05-04-2012

> i'm ok with arrays
So why was the title of the thread "array concepts"?

Consider adding some print statements so you can see what things are doing.

Code:

if (c >= '0' && c <= '9') {
    printf("What is it %d\n", c - '0' );
    ++ndigit[c-'0'];
}

It's source code, you can do whatever you want to it.

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