А нащо рабам щось показувати? Рабам треба наказувати!

Код:

#include <stdio.h>
#include <stdlib.h>

/* run this program using the console pauser or add your own getch, system("pause") or input loop */
void f_numbers1(int n){
  int d1 = 0, d2 = 1, d3;
  if(n == 0)
      printf("%d", n);
  else if(n == 1){
    printf("%d %d", n-1, n);
  }else{
    printf("0 1");
    int i;
    for(int i = 2; i <= n; i++){
      printf("%d ", d3 = d1 + d2);
      d1 = d2;
      d2 = d3;
    }
  }
}
int main(int argc, char *argv[]) {
  
  f_numbers1(15);
  return 0;


}

Помилка:
14    13    D:\проекти с++\main.c    [Error] redeclaration of 'i' with no linkage
14    5    D:\проекти с++\main.c    [Error] 'for' loop initial declarations are only allowed in C99 or C11 mode

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace WindowsFormsApp1
{
    public partial class Form1 : Form
    {
        public Form1()
        {

            InitializeComponent();
            
        }
        
        
        private void button1_Click(object sender, EventArgs e)
        {
            
            }

        private void COPY_Click(object sender, EventArgs e)
        {
            Clipboard.SetText(textBox1.Text);
        }

        private void Slider_Scroll(object sender, EventArgs e)
        {
            label2.Text = "Password Length: " + Slider.Value.ToString();

        }

        private void checkBox1_CheckedChanged(object sender, EventArgs e)
        {
            const string UPPER_CASE = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
        }

        private void checkBox2_CheckedChanged(object sender, EventArgs e)
        {
            const string LOWER_CASE = "abcdefghijklmnopqrstuvwxyz";
        }

        private void checkBox3_CheckedChanged(object sender, EventArgs e)
        {
            const string NUMERIC = "0123456789";
        }

        private void checkBox4_CheckedChanged(object sender, EventArgs e)
        {
            const string SPECIAL_CHARACTERS = @"~!@#$%^&*()+=-";
        }
    }
}