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#include <stdio.h>
/* array1.c - count digits, whitespace, and others */
main()
{
    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);
}
$ gcc array1.c
$ ./a.out < array1.c
digits =  9 4 0 0 0 0 0 0 0 1, white space = 204, other =  356
$
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1. "int ndigit[10]" reserves 10 integers, ndigit[0] through ndigit[9]   
2. chars are just small integers, '0' equals 48 and '9' equals 57 in
   ascii, so [c-'0'] becomes 0 thorugh 9.
3. if (condition1) statement1
   else if (condition2) statement2
   else if (condition3) statement3 
   else statement4
4. No brackets {} for while because it contains a single "statement".
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