what is the function of fflush stdin in c code example

Example 1: string strcat function in c

#include <stdio.h>
#include <string.h>

int main() {
   char str1[100] = "This is ", str2[] = "A Name";

   // concatenates str1 and str2
   // the resultant string is stored in str1.
   strcat(str1, str2);

   puts(str1);
   puts(str2);

   return 0;
}

Example 2: what is stdin in c

//stdin accesses the keyboard, it's a file pointer

Example 3: strcmp in c

#include <stdio.h>
#include <string.h>

int main()
{
    char str1[] = "abcd", str2[] = "abCd", str3[] = "abcd";
    int result;

    // comparing strings str1 and str2
    result = strcmp(str1, str2);
    printf("strcmp(str1, str2) = %d\n", result);

    // comparing strings str1 and str3
    result = strcmp(str1, str3);
    printf("strcmp(str1, str3) = %d\n", result);

    return 0;
}