Math Equation 4

#include <iostream>
#include <vector>
using namespace std;
char s[100];
vector<int> x={3,7,5,4,2};
int y = 15;
int calc (int i, int sum){
-if( i==x.size() )
--return sum==y ;
-s[i]='+';
-if(calc(i+1, sum+x[i]))
--return true;
-s[i]='-';
-if(calc(i+1, sum-x[i]))
--return true;
-return false;
}
int main() {
-if( calc(0,0) ){
--if(s[0]=='-')
---cout<<"-";
--cout<<x[0];
--for(int i=1;i<x.size();++i)
---cout<<s[i]<<x[i];
--cout<<"="<<y<<endl;
-}
-else
--cout<<"No"<<endl;
}