for(int i = 0; i < sizeArray; ++i){
    for(int j = i; j > 0; --j){
        if (s[i].positionX == s[j-1].positionX){
            s[i].positionY = s[j-1].positionY;
        }
    }
}

auto do_work = [&] {
   for(int i = 0; i < sizeArray; ++i){
       for(int j = i; j > 0; --j){
           if (s[i].positionX == s[i-1].positionX){
               s[i].positionY = s[i-1].positionY;
               return;
           }
       }
   }
};

do_work();  //you can call this multiple times if you need to!

[&]
{
   //your code with the added return statement.
}();

for(int i = 0; i < sizeArray; ++i){
    for(int j = i; j > 0; --j){
        if (s[i].positionX == s[i-1].positionX){
            s[i].positionY = s[i-1].positionY;
            i = sizeArray; //it will break the outer loop!
            break;
        }
    }
}

bool stop = false;

for(int i = 0; i < sizeArray; ++i){
    for(int j = i; j > 0; --j){
        if (s[i].positionX == s[i-1].positionX){
            s[i].positionY = s[i-1].positionY;
            stop = true;
            break;
        }
    }
    if (stop) {
        break;
    }
}

bool match = false;

for(int i = 0; i < sizeArray && !match; ++i){
    for(int j = i; j > 0 && !match; --j){
        if ( match = ( s[i].positionX == s[i-1].positionX ) ){
            s[i].positionY = s[i-1].positionY;
        }
    }
}

for(int i = 0; i < sizeArray; ++i){
      int j = i;
      while ( j != 0 && s[i].positionX != s[i-1].positionX ) --j;
      if ( j != 0 ) {
           s[i].positionY = s[i-1].positionY;
           break;
      }
}