Visual Studio 2013 programming "<<" is not matching operands? - c++

Question

I am getting an error saying the operand "<<" (right before times3(x) in the main function ) does not match the operand types being outputted in that line. What am I doing wrong? I searched for errors similar to it and found that its an inclusion error but i thought having would fix it. Also, countdown(seconds) in the main function is not being recognized and giving me an error. Why is that? The problems keep occurring when working with void.
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#include <iostream>
#include <string>
#include <cstdlib>
#include <limits>
using namespace std;
bool die(const string & msg);
double triple(double x);
double times9(double x);
void triple(double & result, double x);
void times3(double & x);
void countdown(unsigned seconds);
bool restore();
int main(){
double x;
cout << "x: " << endl;
cin >> x;
cout << "The triple of " << x << " is " << triple(x) << endl;
cout << "9 times of " << x << " is " << times9(x) << endl;
cout << "3 times of " << x << " is " << times3(x) << endl;
unsigned seconds;
cout << "seconds: " << endl;
cin >> seconds;
cout << countdown(seconds) << endl;
}
bool die(const string & msg){
cout << "Fatal error: " << msg << endl;
exit(EXIT_FAILURE);
}
double triple(double x){
return 3 * x;
}
double times9(double x){
return 3 * triple(x);
}
void triple(double & result, double x){
x = 3 * x;
}
void times3(double & x){
x = triple(x);
}
void countdown(unsigned & seconds){
unsigned count = seconds;
cin >> seconds || die("input failure");
for (unsigned i = seconds; i <= size; i--){
cout << i << endl;
}
cout << "Blast off! " << endl;
}
bool resotre(){
cin.clear();
cin.ignore(numeric_limits<streamsize>::max(), '\n');
return cin.good();
}'

Answer 1

As mentioned in earlier answer, you need to change the return type of your function from void to the data type of variable your trying to print.
Another issue in your code is with function void countdown(unsigned & seconds)
Declaration and definition of the functions are different.
You have declared it as void countdown(unsigned seconds); but at the time of defining it you are using void countdown(unsigned & seconds). In declaration you are declaring it to take arguments by value but in definition you are making it to take arguments by reference.
Also in the for loop of the function countdown you have written
for (unsigned i = seconds; i <= 0; i--), this won't print any output, since your condition is i<=0, i think you tried to type i >= 0. :)

Answer 2

times3 returns void. Try:
times3(x);
cout << "3 times of " << x << " is " << x << endl;
Or have times3() return double instead of passing by reference.
double times3(double x);