Calling a function recursively more than once

Question

I am new to programming, Please explain me the working of the below recursion function. The function is called recursively twice, Will the statements after the 1st recursive call gets executed?

void sort(int low, int high) {
   int mid;

   if(low < high) {
      mid = (low + high) / 2;
      sort(low, mid);
      sort(mid+1, high);
      merging(low, mid, high);
   } else { 
      return;
   }   
}
void main()
{
   sort(0, 10);
}

Answer 1

see the Recursion example link from stack overflow. Examples of Recursive functions

What are you trying to achieve in the code? A recursion function should call the function itself and it should have the condition to stop otherwise it will go in infinite loop. The code you have written called the same function twice and which is not correct. You should call the function once and with stop condition.

Answer 2

Lets go line by line

1. First your sort function will run for arguments 0 and 10 this will be the first call to this function.
2. From line if(low < high) Since 0 < 10 then mid will be 5 : because of mid = (low + high) / 2; .
3. Now again the sort function will run now for args 0 and 5 this will be the second call to this function, but remember the first call is still not finished doing its job.
4. Since 0 < 5 then mid will be 2.
5. Now again the sort function will run this time for args 0 and 2 this will be third call and the second function will remain working.
6. since 0 < 2 mid will be 1.
7. Now again the sort function will run this time for args 0 and 1 this will be forth call and the third call to the function will remain working.
8. since 0 < 1 mid will be 0.
9. Now again the sort function will run this time for args 0 and 0 this will be fifth call and the forth call to the function will remain working.
10. since 0 < 0 is now false the return call in the else will be executed and this function will be destroyed. Now the control will go back to the forth call which was working for args 0 as low and 1 as high.
11. Now from the fifth line sort(mid+1, high); of your code sort will be called again this time for low = 1 and high also = 1.
12. Now again the sort function will be called and this is the sixth call and this time it will run for args low = 1 and high = 1 and it will start executing from the first line of your code.

Consider this as a stack, first push sort(0,10) then => sort(0,5) then => sort(0,2) then => sort(0,1) then => sort(0,0)

Now since sort(0,0) finished executing it will be removed from the stack and sort(0,1) will continue. So it should look like this

sort(0,10) => sort(0,5) => sort(0,2) => sort(0,1)

Again in the fifth line of the sort(0,1) the call to sort() is there, so again sort will be pushed to this stack:

sort(0,10) => sort(0,5) => sort(0,2) => sort(0,1) => sort(1,1)

This will goes on and finally the call to the sort(0,10) will finish executing and you will get your desired outcome.