# C Exercises: Count the number of triangles can be fromed from a given array

## C Array: Exercise-52 with Solution

Write a program in C to count the number of triangles that can be formed from a given array.

**Sample Solution:**

**C Code:**

```
#include <stdio.h>
#include <stdlib.h>
// Comparison function for qsort
int compare(const void* one, const void* two)
{
return *(int*)one > *(int*)two; // Compare two integers
}
// Function to count the number of possible triangles that can be formed
int CountNumberOfTriangles(int *arr1, int arr_size)
{
int ctrTriangle = 0, i, j, k;
qsort(arr1, arr_size, sizeof(int), compare); // Sort the array in ascending order
for (i = 0; i < arr_size - 2; ++i)
{
for (j = i + 1; j < arr_size; ++j)
{
k = j + 1;
// Check for triangles (arr1[i] + arr1[j]) > arr1[k]
while (k < arr_size && (arr1[i] + arr1[j]) > arr1[k])
{
k++;
}
// Increment the count of triangles
ctrTriangle += k - j - 1;
}
}
return ctrTriangle;
}
int main()
{
int arr1[] = {6, 18, 9, 7, 10};
int n = sizeof(arr1) / sizeof(arr1[0]);
int i;
// Print the original array
printf("The given array is: ");
for (i = 0; i < n; i++)
{
printf("%d ", arr1[i]);
}
printf("\n");
// Calculate and print the number of possible triangles that can be formed from the array
printf("Number of possible triangles that can be formed from the array is: %d\n",
CountNumberOfTriangles(arr1, n));
return 0;
}
```

Sample Output:

The given array is : 6 18 9 7 10 Number of possible triangles can be formed from the array is: 5

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