问使用C中的scanf退出do while循环at !=EOF将进行3次额外的迭代

EN

g++ eda.c -o eda.exe
./eda.exe < eda.txt

3
[9.3,1.2,87.9]
[1.0,1.0]
[0.0,0.0,1.0]
print v3
incr v3 v1

do {
        //sscanf (mystring,"%s",str);
        //int res = strncmp(str, "incr", 10);
        if(mystring[0] == 'p') casenumber = 1;
        else if(mystring[0] == 'i') casenumber = 2;
        else if(mystring[0] == 'd' && mystring[1] == 'o') casenumber = 3;
        else if(mystring[0] == 'd' && mystring[1] == 'i') casenumber = 4;
        else if(mystring[0] == 'd' && mystring[1] == 'e') casenumber = 5;

        switch(casenumber)
        {
        case 1 :
            printf("print!\n" );
            break;
        case 2 :
            printf("increase!\n");
            break;
        case 3 :
            printf("dot!\n");
            break;
        case 4 :
            printf("distance!\n");
            break;
        case 5 :
            printf("decr!\n");
            break;
       default :
            printf("casenumber value is: %d\n", casenumber);
            break;
        }
        casenumber = 0;
    } while (fgets (mystring , 21 , stdin) != NULL);