Не робит

#include <stdio.h>
#include <string.h>
#include <conio.h>
#include <stdlib.h>
int main()
{
	int k = 0;
	FILE* F;
	char str[100];
	char FILEName1[20];
	char FILEName2[20];
	puts("Enter first file name");
	gets_s(FILEName1, 20);
	fopen_s(&F, FILEName1, "w+t");
	puts("Enter strings");
	int b = 0;
	while (gets_s(str, 100), strlen(str) != 0)
	{
		fputs(str,F);
		fputs("\n", F);
	}
	rewind(F);
	puts("FileF");
	while (fgets(str, 100, F) > 0)
	{
		puts(str);
	}
	rewind(F);
	FILE* G;
	puts("Enter second file name");
	gets_s(FILEName2, 20);
	fopen_s(&G, FILEName2, "w+t");
	fseek(F, 0, SEEK_SET);
	fgets(str, 100, F);
	b = atoi(str);
	fseek(F, 0, SEEK_END);
	fgets(str, 100, F);
	b += atoi(str);
	sprintf_s(str, "%d", b);
	fputs(str, G);
	fclose(F); fclose(G);
	puts("Elements of file G");
	fopen_s(&G, FILEName2, "r+t");
	int num = 1;
	while (fgets(str, 100, G) > 0)
	{
		printf_s("string order %d     ", num);
		puts(str);
	}
	fclose(G);
	return(0);
}