For loop with multiple variable - c++

Question

Is it possible for a for loop with 2 variables to stop incrementing only one of the variable when a condition is met ? For example
for(int i = 0, j = 0; i < 5 && j < 10; i++, j++)
{
cout << i << " " << j << endl;
}
and the output would look something like
0 0
1 1
2 2
3 3
4 4
4 5
4 6
4 7
4 8
4 9
This is my actual code. I wanted the condition for both variables
cout << sp.dets.size() << " " << gt.groundtruth.size() << endl;
for (int i = 0, j = 0; i < sp.dets.size() && j < gt.groundtruth.size(); j < gt.groundtruth.size() ? j++ : j, i < sp.dets.size() ? i++ : i)
{
cout << i << " " << j << endl;
}
sp.dets.size = 0
gt.groundtruth.size() = 8
It would be nice if the solution works for any number i.e. i > j or i < j or i = 0 or j = 0

Answer 1

You can use ternary statement to increment variable i value. Like below:
for(int i = 0, j = 0; i < 5 && j < 10; j++, i<4? i++: i)
{
cout << i << " " << j << endl;
}
This will output the expected result.

Answer 2

Something like this may work,
int k = 0;
int val = 4;
for(int i = 0, j = 0; i < 10 && j < 10; i++, j++){
if (i>=val){
k=val;
cout << k << " "<< j << endl;
}
else
cout << i << " " << j << endl;
}
Prints this,
0 0
1 1
2 2
3 3
4 4
4 5
4 6
4 7
4 8
4 9

Answer 3

Don't try to be overly clever by trying to fit all the logic in one line. It't more important that your code can be read by others (and yourself in two weeks' time) than saving a single line. If the incrementing logic of the two variables is more complex than just increasing by one for each loop, put them in seperate lines, like this:
while (i<5 && j<10) {
...
// complicated expression calculating new i
// complicated expression calculating new j
}
In your case, you might also flip the logic around:
for (int i=0; i<max(sp.dets.size(), gt.groundtruth.size(); i++) {
cout << min(i, sp.dets.size()-1)
<< ","
<< min(i, gt.groundtruth.size()-1)
<< endl;
}

Answer 4

You can use ternary operator on both variables. Just be sure to change your condition to break only when both reach their destined value
for (int i = 0, j = 0;
i != 5 || j != 10;)
{
i += i < 5 ? 1 : 0;
j += j < 10 ? 1 : 0;
}
You'll note I moved the increment into the loop body, this improves readability, in my opinion.