I am trying to use c++ to sum 3 integers from the input, but I keep get 0. Please help thx.
vector<int> x;
x.reserve(3);
cin >> x[0] >> x[1] >> x[2];
int sum = std::accumulate(x.begin(), x.end(), 0);
cout << sum << endl;
return 0;
1
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3
0
vector::reserve(size_type n) will request a change in the capacity of the vector, not the size. You can use the resize function, or even better the constructor.
int main()
{
std::vector<int> x(3,0); //set the size to 3 and fill with zeros.
std::cin >> x[0] >> x[1] >> x[2];
int sum = std::accumulate(x.begin(), x.end(), 0);
std::cout << sum << std::endl;
}
You can read this answer here for the differences between reserve vs resize.
Fill your vector first with something if not you will probably get undefined
vector<int> x(3,0);
use c++ to sum 3 integers from the input why accumulate always return 0
This answer uses push_back(), and does not need to know how many integers are input, as the vector will auto expand; In this way it sidesteps the issues of std::vector that were defeating your code.
Consider that, because a "how many int" might be submited is seldom fixed you are more likely to want to count how many input "on the fly". So perhaps use a loop, cin to a local var, then x.push_back( a_local_var), and repeat until some condition (maybe eof(), or local var == -1, etc.) x.size() is your counter.
Here is a functioning example, using command line vars and eof() (and a vector and accumulate).
// Note: compile with -std=c++17 for the using comma list
#include <iostream>
using std::cout, std::cerr, std::endl, std::hex, std::dec, std::cin, std::flush; // c++17
#include <vector>
using std::vector;
#include <string>
using std::string;
#include <sstream>
using std::stringstream;
#include <numeric>
using std::accumulate;
#include <cassert>
class T951_t // ctor and dtor compiler provided defaults
{
public:
int operator()(int argc, char* argv[]) { return exec(argc, argv); } // functor entry
private:
stringstream ssIn; // to simulate user input
int exec(int argc, char* argv[])
{
int retVal = initTest(argc, argv); // transfer command line strings into ssIn
if(retVal != 0) return retVal;
// ------------------------------------------------------------
// simulate unknown quantity of ints
vector<int> x;
do {
int localInt = 0;
ssIn >> localInt;
if(!ssIn.good()) // was transfer ok?
{ // no
if (ssIn.eof()) break; // but we tolerate eof
// else err and exit
cerr << "\n !ssIn.good() failure after int value "
<< x.back() << endl;
assert(0); // harsh - user typo stops test
}
x.push_back(localInt); // yes transfer is ok, put int into vector
//cout << "\n " << localInt; // diagnostic
} while(true);
showResults(x);
return 0;
}
// this test uses a stringstream (ssIn) to deliver input to the app
// ssIn is initialized from the command line arguments
int initTest(int argc, char* argv[])
{
if (argc < 2) {
cerr << "\n integer input required" << endl;
return -1;
}
// test init
for (int i=1; i < argc; ++i) {
// cout << "\n " << argv[i]; // diagnostic
ssIn << argv[i] << " "; // user text into stream
}
cout << endl;
return 0;
}
// display size and contents of vector x
void showResults(vector<int> x)
{
cout << "\n x.size(): " << x.size() << endl;
int sum = std::accumulate(x.begin(), x.end(), 0);
for (auto i : x)
cout << " " << i;
cout << endl;
cout << "\n sums to: " << sum << '\n' << endl;
}
}; // class T951_t
int main(int argc, char* argv[]) { return T951_t()(argc, argv); } // call functor
Tests:
./dumy951 1 2 3 55 12345678900 <-- fail after 55 because last int too big
./dumy951 1 2 3 y 55 12345678900 <-- fail after int value 3 (invalid int)
./dumy951 1 2 3 4 5 6 7 8 9 10 <-- success, result is 55
