Debugging a function in C - c

Question

This function takes an integer array, the number of elements
in the array and tries to find a majority element in the
array. If the majority element exists, it is placed in
*result and the function returns true.
If no majority element exists, then the function returns
false. In that case, *result should not be used.
My output isn't working correctly for the program I'm writing and it is because of this findMajority function I think.
This is what the output is supposed to look like: http://pastebin.com/Q5ycXHrg
This is what my output looks like: http://pastebin.com/7P1ZTpML
This is the input:
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2
1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2
1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2
1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 1
1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2
1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 3
1 1 2 2 1 1 2 2 1 1 2 2 1 1 2 2 1 1 2 2 1 1 2 2 1 1 2 2 1 1
1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9 1
1 2 3
1 1 1
1 2 1
1 2
1 1
2
1 1 1 1 2 3 4 5 6 7
Here is the function:
int findMajority(int *array, int count, int *result){
int i, counter, bcount = 0, ccount = 0, candidate, j;
if(count == 1) {
*result = *array;
return true;
}
if(count % 2 != 0 ) {
for(i = 0; i < count; i++) {
if(*(array + i) == *(array + count)) {
counter++;
}
}
if(counter > (count/2)) {
*result = *(array + count);
return true;
}
else {
*(array + count) = 0;
count--;
}
}
for(j=0; j <= count; j += 2) {
if(*(array + j) == *(array + (j + 1))) {
*(array + (count + 1)) = *(array + j);
bcount++;//how many numbers on the end of the array
}
}
if(bcount == 1) {
int k = count;
while(*(array + k) == 0) {
candidate = *(array + k);
}
}
else
findMajority((array + count), count, result);
for(j=0; j <= count; j += 2) {
if(*(array + j) == candidate) {
ccount++;
}
}
if(ccount > (count/2)) {
*result = candidate;
return true;
}
else
return false;
}

Answer 1

Your function has a lot of problem.
Without intialising counter you are incrementing it
check whether array[count] is the valid last element or array[count-1] is the correct one
In this code for(j=0; j <= count; j += 2){
if(*(array + j) == *(array + (j + 1))){
*(array + (count + 1)) = *(array + j);
bcount++;//how many numbers on the end of the array
}}
for count= 3 you are accessing array[4] array[5] etc.
And this is a infinite loop. you are not modifying condition variable inside the loop while(*(array + k) == 0) { candidate = *(array + k); }

Answer 2

I suggest you learn how to use a debugger to debug your program. For example, after wrapping your code with the following:
#include <stdio.h>
typedef enum { false, true } boolean;
// ((( your function here )))
int main(int argc, char* argv[])
{
int result = 0;
int number = 0;
int test[] = { 1, 1, 1, 1, 1, 1, 1 };
result = findMajority(&test[0], sizeof(test) / sizeof(int), &number);
printf("Result = %d, Number = %d\n", result, number);
return 0;
}
Assuming you put this into 'question.c' you could then issue the commands (assuming you have gcc and gdb):
$ gcc -g -o question question.c
$ gdb ./question
(gdb) b findMajority
Breakpoint 1 at 0x80483ea: file question.c, line 6.
(gdb) run
Starting program: ./question
Breakpoint 1, findMajority (array=0xbffff4bc, count=7, result=0xbffff4d8) at question.c:6
6 int i, counter, bcount = 0, ccount = 0, candidate, j;
You can then use the n command to step to the next line, and the p command to print variables to see what's going wrong. For example, you could find some of the problems that Toms pointer out relatively quickly:
39 while(*(array + k) == 0){
(gdb) n
40 candidate = *(array + k);
(gdb) n
39 while(*(array + k) == 0){
(gdb) n
40 candidate = *(array + k);
(gdb) n
39 while(*(array + k) == 0){
(gdb) n
There's your infinite loop.
(gdb) p counter
$3 = -1207959944
And there's your uninitialized counter.
Part of learning programming is figuring out strategies of determining just what went wrong. Some people like to use text-based debuggers like gdb. Some people like graphical debuggers like you could find in Eclipse CDT. Some people put printf() statements throughout their code.
Once you're really good, like Toms, you can just read it and rattle off the problems. ;-)