fflush use?

char.c

#include <stdio.h>
#define MAXSIZE 256
void read_string(char* p);

int main(void) {

    char c, s[MAXSIZE];

    puts("I/O lib");
    puts("");

    printf("Please give me a char: ");
    c = getchar();
    printf("What you keyin is %c\n", c);
//    fflush(stdin);
    while(getchar()!='\n');

    printf("Please give me a string : ");
    read_string(s);
    printf("What you keyin is %s\n", s);

    printf("\n Press <Enter> to continue...");
    while ((c=getchar()) != '\n');

    return 0;
}

void read_string(char* p) {
    int i;
    char c;
    for (i=0; i<MAXSIZE-1; ++i) {
        if ( (c=getchar()) != '\n' ) {
            p[i] = c;
        } else {
            break;
        }
    }

    p[i] = '\0';
}