You can use Kadane’s Algorithm:

```
Initialize:
max_so_far = 0
max_ending_here = 0
Loop for each element of the array
(a) max_ending_here = max_ending_here + a[i]
(b) if(max_ending_here < 0)
max_ending_here = 0
(c) if(max_so_far < max_ending_here)
max_so_far = max_ending_here
return max_so_far
```

Sample Code

```
#include<iostream>
using namespace std;
int maxSubArraySum(int a[], int size)
{
int max_so_far = 0, max_ending_here = 0;
for (int i = 0; i < size; i++)
{
max_ending_here = max_ending_here + a[i];
if (max_ending_here < 0)
max_ending_here = 0;
if (max_so_far < max_ending_here)
max_so_far = max_ending_here;
}
return max_so_far;
}
int main()
{
int a[] = {2, -1, 2, 4, 6, -5};
int n = sizeof(a)/sizeof(a[0]);
int max_sum = maxSubArraySum(a, n);
cout << "Maximum contiguous sum is \n" << max_sum;
return 0;
}
```

Credit: http://www.geeksforgeeks.org/largest-sum-contiguous-subarray/