c++ - Running an infinite loop because of next_permute -

i trying solve problem input 2 vectors of different lengths , add scalar product. minimun scalar product problem https://code.google.com/codejam/contest/32016/dashboard#s=p0 . i'm apparently hopelessly running infinite loop.probably because of permutation.but don't understand why .

#include "stdafx.h"; #include <algorithm> #include <fstream> using namespace std;  //output stuff int cases[100]; int casesol[100]; int ncase; void output() {     (int = 1; <= ncase; i++)     {         printf("case #%d: %d\n", i, casesol[i]);     } }  //output stuff end int product; int v1[100]; int v2[100]; int minimum; int main() {      // read in number of cases     freopen("file.in", "r", stdin);     freopen("file.out", "w", stdout);     scanf("%d", &ncase);      // read in misc problem constants     (int = 1; <= ncase; ++i) {         int vector_size;         scanf("%d", &vector_size);          // read in data          //v1= new int [vector_size];         //v2=new int [vector_size];          (int j = 0; j < vector_size; ++j){             scanf("%d", &v1[j]);         }         (int j = 0; j < vector_size; ++j){             scanf("%d", &v2[j]);         }          // problem solving logic here         do{             (int j = 0; j < vector_size; ++j){                 product += v1[j] * v2[j];             }             if (product<minimum)                 minimum = product;         } while (next_permutation(v2 + 0, v2 + (vector_size - 1)));         casesol[i] = minimum;     }     output();     return 0; } 

the comment @nathanoliver made correct. think problem here in design. there easier solution problem looking at; minimum scalar vector max of 1 vector multiplied times min of other vector. consider code below:

const int size = 3;  std::vector<int> v1 {1, 3, -5}; std::vector<int> v2 {-2, 4, 1};  std::sort(v1.begin(), v1.end()); std::sort(v2.begin(), v2.end());  int product = 0; (int = 0; < size; i++) {     product += v1[i] * v2[size-1-i]; } 

this first example page linked (hard coded instead of reading file). result correct, -25.