---------- Post updated at 09:57 AM ---------- Previous update was at 09:36 AM ----------
btw i still hav a question abt tis program, it is a program to count then number of occurrences of each digit. At the "while" part, why shud we nid to put [c-'0'] and not [c] for the ++ndigit to execute tis program?
Code:
#include <stdio.h>
int main()
{
int i, c;
int ndigit[10];
for (i = 0; i < 100; ++i)
ndigit[i] = 0;
while ((c = getchar()) != EOF)
++ndigit[c-'0'];
printf("digits =");
for (i = 0; i < 10; ++i)
printf(" %d", ndigit[i]);
}
In addition to what Corona688 has already said, I need to comment on other aspects of your program. Any results that you get from this code are unreliable and suspect. First let me add line numbers to your C code for reference in the remainder of my comments:
Code:
1 #include <stdio.h>
2
3 int main()
4 {
5 int i, c;
6 int ndigit[10];
7 for (i = 0; i < 100; ++i)
8 ndigit[i] = 0;
9
10 while ((c = getchar()) != EOF)
11 ++ndigit[c-'0'];
12
13 printf("digits =");
14 for (i = 0; i < 10; ++i)
15 printf(" %d", ndigit[i]);
16 }
If you would move line 6 to come after line 1 but before line 3 (making the array global instead of local) or if you would declare the array to be static, the array would be guaranteed to be initialized to 0 without needing the for loop on lines 7 and 8 to initialize the array.
Clearing the 1st 100 elements of an array of 10 elements (as you do on lines 7 and 8) will overwrite other data in your address space (or attempt to write into unallocated space causing your program to crash). You might be lucky and not overwrite anything useful, but once you try to set ndigits[10] to 0 the results of this program are undefined. On some combinations of hardware architecture and C compiler design it would be common for this construct to overwrite the value of i while processing this loop (thereby turning lines 7 and 8 into an infinite loop).
You are reading data from an unknown source. If there is any character read from standard input by this program that is not a numeric digit, if an end-of-file condition is detected by getchar() while it tries to read 100 bytes from standard input, or if an error is detected while getchar() tries to read 100 bytes from standard input, you will again try to modify an integer value that is outside space allocated to the ndigits[] array. If that happens, the behavior of your program is undefined.
Most applications like this one produce text files that can be processed reliably by all of the UNIX/Linux text processing utilities. Since this program does not terminate its output with a <newline> character, the output is not a text file. If the output is just intended to be viewed by a human at a terminal, that might not be a problem, but the user will be disappointed to see that the shell prompt for the next command to be run starts in the middle of a line (possibly making the count you report for the number of '9' characters found ambiguous depending on the value of you shell's current setting for its command prompt).
I don't want to scare you off from programming, but realize that programming is an art and a science. Attention to tiny details is crucial when writing programs.
Last edited by Don Cragun; 12-04-2012 at 01:37 PM..
Reason: fixed 2 typos
These 2 Users Gave Thanks to Don Cragun For This Post:
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