While writing what should be a very simple program ( out of K&R C book ), I get some output which I do not understand. If I EOF right away, nl_count is correctly 0, but space_count is always 32767 ( half of maximum int range), and tab_count is a large value ( usually very high or very low ).
When I initialize all variables to 0, then the program works correctly. What am I missing here?
10 int main(void)
11 {
12 int tab_count, space_count, nl_count;
13
14 //tab_count = space_count = nl_count = 0;
15
16 int c;
17 while( (c = getchar()) != EOF ){
18 if( c == '\t' )
19 tab_count++;
20 if( c == ' ' )
21 space_count++;
22 if( c == '\n' )
23 nl_count++;
24 }
25
26 printf("\n");
27 printf("TABS = %d\n", tab_count);
28 printf("SPACES = %d\n", space_count);
29 printf("NEWLINES = %d\n", nl_count);
30
31 return 0;
32 }
Inputs and Outputs:
Here is another input, which again correctly outputs 3 for newlines, but junk for tabs, and 32767 for spaces.
(space)(space)(space)\t\t\t\n\n\n
TABS = 441446448
SPACES = 32767
NEWLINES = 3
When I initialize all vars to 0, then the program works correctly. What am I missing here?
tab_count, space_count and nl_count; are automatic storage variables. If you don't initialize them to 0, they have a indeterminate values. Reading from them is technically undefined behaviour (UB). Since you're incrementing their value before initializing them, you are invoking UB. One manifestation of UB is to produce seemingly nonsensical values.