graphsin.cpp

#include <cmath>
#include <iostream>
#include <string>
#include <vector>

int main()
{
  int size = 80, height = 21;

  // Start with an empty chart (lots of spaces and a line in the middle)
  std::vector<std::string> chart(height, std::string(size, ' '));
  chart[height/2] = std::string(size, '-');

  // Then just put x-es where the function should be plotted
  for(int i = 0; i < size; i++) {
    chart[static_cast<int>(std::round(10 * std::sin(i / 4.5) + 10))][i] = '*';
  }

  // and print the whole shebang
  for(auto &&s : chart) {
    std::cout << s << '\n';
  }
}