c++ – Local function definition are illegal

c++ – Local function definition are illegal

You have the functions Test and TestTwo inside your main function.

Define your functions outside the main routine.

c++ – Local function definition are illegal

While local function definitions as above are illegal C++ supports local functions by means of lambdas. The following is legal in C++11 and later.

#include <iostream>
using namespace std;

int main()
{
    auto TimesTwo = [](int num1)
    {
        int result;
        result = num1 * 2;

        return result;
    };

    auto Test = [&TimesTwo](int a)
    {
        int result;
        int num1;
        cin >> num1;
        result = TimesTwo(num1);
        return result;
    };

    using fp = int (*)(int);
    fp f1 = TimesTwo; // non-capturing lambda can be converted to function pointer.
    
    return 0;
}

A helpful feature of lambdas is that lambdas that do not capture anything can be converted to a function pointer.