c++ - swap function in quick sort gives wrong output -

swap function quick sort. gives wrong output. when use temporary variable gives correct output. here tester:

void swap(int &a,int &b){     a=a+b;     b=a-b;     a=a-b; } 

this works fine though:

void swap(int &a,int &b){     int temp=a;     a=b;     b=a; } 

i passing array elements function inside partition function of quick sort algorithm.

your code swap without 3rd variable looks ok. unfortunately, algorithm cannot applied swapping value itself, example:

void swap(int &a,int &b){   // &a == &b, value 123     a=a+b;                  // == b == 246     b=a-b;                  // == b == 0 (oops!)     a=a-b;                  // == b == 0  } 

also, please note there's standard function swapping (std::swap) , code, if compiled without optimization, works slower usual swap (with 3rd variable) performs more memory operations. also, code may lead integer overflow or underflow undefined behavior standard , may or may not work expect. if add readability issue (the important thing) list, recommendation just don't use swap without 3rd variable.