limited input from user in struct

help please this doesnt work properly

input
omayma.firstname : AAAAAAAAAAAAAAAAAAAAAAAAAAA
omayma.lastname : BBBBBBBBBBBBBBBBBBBBBBBBBBBB
output :
omayma.firstname : AAAAAAAAAABBBBBBBBBB
omayma.lastname : BBBBBBBBBB
expected output :
omayma.firstname : AAAAA (10 A exatcly)
omayma.lastname : BBBBBB (10)

typedef struct
{
    char firstname[10];
    char lastname[10];
} person;

int main()
{
    person omayma;
    printf("firstname : ");
    scanf("%10s", omayma.firstname);
    fflush(stdin);
    printf("lastname : ");
    scanf("%10s", omayma.lastname);
    fflush(stdin);
    puts(omayma.firstname);
    puts(omayma.lastname);
    return 0;
}

Suggestions to get your code to work as you probably expected it to.

First, provide more space for names. space is cheap. Go big (enough) in struct:

typedef struct
{
    char firstname[50];
    char lastname[50];
} person;

Second, if you have to use scanf(), make the follow on adjustments for larger buffers...

scanf("%49s", omayma.firstname);// adds room for long names, 

Or, you can get rid of scanf() altogether with what may be a better alternative:

fgets(omayma.firstname, sizeof omayma.firstname, stdin);
omayma.firstname[strcspn(omayma.firstname, "\n")] = 0;//remove newline
fgets(omayma.lastname, sizeof omayma.lastname, stdin);
omayma.lastname[strcspn(omayma.lastname, "\n")] = 0;//remove newline

printf("%s %s", omayma.lastname, omayma.lastname);



           

Third, fflush() is only used for output streams:

fflush(stdin);//delete this statement (everywhere)