Sub Grouping algorithm - c

Question

Recently, someone asked me to make a C program that "groups" (his words, not mine!) numbers into pairs.
Here's how it works.
First, the user inputs the maximum range:(let's say) 10
Now, user inputs a number: (let's say) 4.
Then, the program groups 4 and 5 together. (ie. n and n+1)
Next User Input: 8
The program groups 8 and 9 as well.
Now, this goes on.
Exceptions: If the user enters a number that has already been grouped, like 4,5,8 or 9. Then the group which it belongs to gets removed altogether. Also, the program invalidates inputs that require pairing with numbers that are already paired. Eg. If 4 and 5 are paired, 3 is not a valid input.
Also, entering the extremes (here, 1 and 10) is not allowed.
I made the above program in C, using Visual Studio 2013. I have provided the code below.
My questions are:
A) How could I have made my code considerably better?(Apart from initializing the array AFTER accepting the max input)
B) More importantly, can someone tell me what this algorithm is? Is this a standard problem? Does it have any real world application/implementation? Or is it just some random idea?
#include<stdio.h>
#inlcude<conio.h>
#define array_size 10
int group[array_size][2] = { 0 };
int n = 0, max=0, search = 0, max_mem = 0;
int tcount = 2;
void sort(int x[][2]);
void print_groups();
void test_print();
void main()
{
group[0][0] = 0;
group[0][1] = 1;
printf("Enter a number:");
scanf_s("%d", &max);
max_mem = (max/2)+1;
if (max_mem > array_size)
{
printf("Not enough memory assigned!");
return;
}
else
{
group[max_mem-1][0] = max;
}
print_groups();
test_print();
while (1)
{
printf("Enter a number:");
scanf_s("%d", &n);
if ((n <= 1) || (n >= max-1))
{
printf("Invalid entry!");
continue;
}
search = 0;
for (int i = 1; i < max_mem; i++)
{
for (int j = 0; ((j < 2)&&(search!=1)); j++)
{
if (n == group[i][j])
{
group[i][0] = 0;
group[i][1] = 0;
search = 1;
}
if (group[i][0]==n+1)
{
printf("Already group exists -> (%d,%d)", group[i][0], group[i][1]);
//getch();
search = 1;
}
}
}
if (search != 1)
{
group[1][0] = n;
group[1][1] = n + 1;
}
printf("\nSorting!\n");
sort(group);
//clrscr();
print_groups();
test_print();
}
}
void sort(int x[][2])
{
int i, j, t[1][2];
for (i = 1; i <= max_mem - 2; i++)
for (j = 2; j <= max_mem-1 - i; j++)
if (x[j - 1][0] >= x[j][0])
{
t[0][0] = x[j - 1][0];
x[j - 1][0] = x[j][0];
x[j][0] = t[0][0];
t[0][1] = x[j - 1][1];
x[j - 1][1] = x[j][1];
x[j][1] = t[0][1];
}
}
void print_groups()
{
printf("The group is:\n%d ", group[0][1]);
for (int i = 1; i < max_mem-1; i++)
{
if (group[i][0] != 0)
{
printf("(");
printf("%d,", group[i][0]);
printf("%d", group[i][1]);
printf(")");
}
}
printf(" %d.", group[max_mem - 1][0]);
printf("\n");
}
void test_print()
{
printf("Array Formation:\n");
for (int i = 0; i < array_size; i++)
{
printf(" %d,%d ", group[i][0], group[i][1]);
}
printf("\n");
}

Answer 1

Sounds like it's just some random idea. You can simplify your code by using a one-dimensional array, where each entry in the array is
0 for numbers not in a group
1 for the first number of a group
2 for the second number of a group
For example, if array[4] is 1 and array[5] is 2, then 4 and 5 are a group.
When the user enters a new number, it's easy to update the array. Here's an example in pseudo-code of how the array would be updated if the user enters the number 7
if (array[7] == 0 and array[8] == 0)
array[7] = 1, array[8] = 2
else if (array[7] == 0 and array[8] == 1)
input is invalid
else if (array[7] == 1)
array[7] = 0, array[8] = 0
else if (array[7] == 2)
array[6] = 0, array[7] = 0