How can I insert a certain word into a string at the place I need?

Question

C++ / C#

Greetings to all! The following task is on the agenda: "Develop a function that inserts a given word into a sentence. The new word should become the nth word in the sentence (n is given as the third parameter of the function). From the keyboard, enter three character strings and a word. Using the developed function, insert an additional word into the entered lines so that in the first line it becomes the first, in the second - the third, and in the last - the fifth"

There are no problems with the first sentence. But with the second and third, it does not work out. I tried to count the number of spaces in sentences, but it doesn't even work.

Tell me where and what is wrong?
Thanks in advance to everyone who will answer)))

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
# define MAX 1000

struct Stroka{
  char First[100];
  char Second[100];
  char Third[100];
  char Word[20];
}list[MAX];

int i = 0;
void Poshuk();
void Poshuk1();
void Poshuk2();

int main(){

  for (i; i < 1; i++) {
    system("chcp 1251");
    printf("Первое предложение: ");
    gets_s(list[i].First);
    printf("Второе предложение: ");
    gets_s(list[i].Second);
    printf("Третье предложение: ");
    gets_s(list[i].Third);
    printf("Слово: ");
    gets_s(list[i].Word);
    getchar();
  }

  Poshuk();
  Poshuk1();
  Poshuk2();

  return 0;
}

void Poshuk() {
  for(int j = 0; j < i; j++) {
    printf_s("Обработанное: %s %s", list[j].Word, list[j].First);
  }
  getchar();
}

void Poshuk1() {
  char* p2 = list[i].Word, * p1 = list[i].Second;
  for (int i = 0; i < 3; i++) {
    if (*p1 == ' ') {
      p1++;
    }
  }
  strcpy(p1, p2);
  printf_s("Обработанное: %s", &p1);
  getchar();
}

void Poshuk2() {
  char* p2 = list[i].Word, * p1 = list[i].Third;
  for (int i = 0; i < 5; i++) {
    if (*p1 == ' ') {
      p1++;
    }
  }
  strcpy(p1, list[i].Word);
  printf_s("Обработанное: %s", &p1);
  getchar();
}

Answer 1

Not so in almost every line.
First, why do you need a four-line structure? What for to you an array from it on 1000 elements.
What the hell is this all about?
for (i; i < 1; i++) {
Does this cycle of one iteration bother you at all?
Further, the assignment clearly states

Develop a function that inserts a given word into a sentence. The new word must become the nth word in the sentence (n is given as the third parameter of the function)

Those. you need to take one function, and call it 3 times with passing there 1, then 2, then 5, and not write 3 Poshuks.
Further, in all your functions you refer to list[] at different indexes, but you only have one first element of the array entered (again, why the hell do you need a whole array of structures if exactly 3 lines and one word are given in the task?!)
And the last , the logic of the desired function should be as follows: We go through the passed string, counting how many spaces we met. As soon as we meet a space with a given number, we shift all the characters behind this space to the right by the length of the inserted word, then we copy the word to an empty place.
To shift characters in a string, you first need to find its length, then loop back to the last shifted index with length + k and assign the value of the character at index ik to the current character.