check-input

/* input & check validation*/
    while (1) {
        printf("Enter epsi: ");
        fflush(stdin); ch = '\0';
        scanf("%d%c", &a, &ch);
        if (a>0 && ch == '\n') {
            break;
        }
        else {
            printf("Invalid input, please re-enter!\n");
        }
    }