[Bug c++/96538] New: Integer overflow when there are multiple operands in addition operation.

[Bug c++/96538] New: Integer overflow when there are multiple operands in addition operation.

[prateek_kd at yahoo dot co.in]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96538

            Bug ID: 96538
           Summary: Integer overflow when there are multiple operands in
                    addition operation.
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: prateek_kd at yahoo dot co.in
  Target Milestone: ---

I am trying to add int values present in the vector and store in long int type
variable. If I am using for  loop for calculating the sum of vector elements
program produces correct sum. However if If I perform direct addition(e.g sum=
arr[0]+arr[1]...=arr[n]), the results obtained is incorrect and seems that
overflow is occurring. Below is the code snippet for you reference:

Input:942381765 627450398 954173620 583762094 236817490


Code leading to overflow/error: 
#include<bits/stdc++.h>
using namespace std;

int main()
{
vector<int> arr(5);
for(int i=0;i<5;i++)
{
cin>>arr[i];
}
sort(arr.begin(),arr.end());
long int  sum = 0,min_sum=0,max_sum=0;
sum = arr[1]+arr[2]+arr[3]
min_sum = arr[0]+ sum; 
max_sum = arr[4]+ sum;
cout<<min_sum<<" "<<max_sum<<endl;

return 0;
}


Output :-1904555549 -1187199419

Code producing correct output:

#include<bits/stdc++.h>
using namespace std;

int main()
{
vector<int> arr(5);
for(int i=0;i<5;i++)
{
cin>>arr[i];
}
sort(arr.begin(),arr.end());
long int  sum = 0,min_sum=0,max_sum=0;
for(int j=0;j<5;j++)
{
sum = sum+ arr[j];//after for loop sum = arr[1]+arr[2]+arr[3]
}
min_sum = arr[0]+ sum; 
max_sum = arr[4]+ sum;
cout<<min_sum<<" "<<max_sum<<endl;

return 0;
}



Output(for same input as above):
3581402857 4298758987

[Bug c++/96538] Integer overflow when there are multiple operands in addition operation.

[prateek_kd at yahoo dot co.in]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96538

--- Comment #1 from Prateek Khade <prateek_kd at yahoo dot co.in> ---
(In reply to Prateek Khade from comment #0)
> I am trying to add int values present in the vector and store in long int
> type variable. If I am using for  loop for calculating the sum of vector
> elements program produces correct sum. However if If I perform direct
> addition(e.g sum= arr[0]+arr[1]...=arr[n]), the results obtained is
> incorrect and seems that overflow is occurring. Below is the code snippet
> for you reference:
> 
> Input:942381765 627450398 954173620 583762094 236817490
> 
> 
> Code leading to overflow/error: 
> #include<bits/stdc++.h>
> using namespace std;
> 
> int main()
> {
> vector<int> arr(5);
> for(int i=0;i<5;i++)
> {
> cin>>arr[i];
> }
> sort(arr.begin(),arr.end());
> long int  sum = 0,min_sum=0,max_sum=0;
> sum = arr[1]+arr[2]+arr[3]
> min_sum = arr[0]+ sum; 
> max_sum = arr[4]+ sum;
> cout<<min_sum<<" "<<max_sum<<endl;
> 
> return 0;
> }
>       
> 
> Output :-1904555549 -1187199419
> 
> Code producing correct output:
> 
> #include<bits/stdc++.h>
> using namespace std;
> 
> int main()
> {
> vector<int> arr(5);
> for(int i=0;i<5;i++)
> {
> cin>>arr[i];
> }
> sort(arr.begin(),arr.end());
> long int  sum = 0,min_sum=0,max_sum=0;
> for(int j=1;j<4;j++)
> {
> sum = sum+ arr[j];//after for loop sum = arr[1]+arr[2]+arr[3]
> }
> min_sum = arr[0]+ sum; 
> max_sum = arr[4]+ sum;
> cout<<min_sum<<" "<<max_sum<<endl;
> 
> return 0;
> }
> 
> 
> 
> Output(for same input as above):
> 3581402857 4298758987

[Bug c++/96538] Integer overflow when there are multiple operands in addition operation.

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96538

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |INVALID

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
There is NO BUG here:
sum = arr[1]+arr[2]+arr[3];

Is done in integer type and then casted to long.
that is it is the same as:
sum = (long)(arr[1]+arr[2]+arr[3]);

While:
for(int j=0;j<5;j++)
{
sum = sum+ arr[j];
}
Is Done in long type.

You can fix the original code by doing:
sum = ((long)arr[1])+((long)arr[2])+((long)arr[3]);