Exercise in C with if and switch statements: Write code to convert 2 digit numbers into words

There's this exercise I'm trying to figure out. The assignment asks to convert a two-digit number in words, the output should be something like this :

Enter a two-digit number:45
You entered the number forty-five.

I'm still a total beginner to programming. I'm at this chapter in this C programming book, in the exercise section about the switch and if statements. The exercise suggests to use two switch statements, One for the tens and the other one for units, but numbers within 11 and 19 require special treatment.

The problem is that I'm trying to figure out what should I do for numbers between 11 and 19, I was thinking to use the if statement but then the second switch function would include in the output and it would turn into something like You've entered the number eleven one.

This is the program I've been writing so far (incomplete):

    int digits;

    printf("Enter a two-digit number:");

    scanf("%d", &digits);

    printf("You entered the number ");

    switch (digits / 10) {
    case 20:
        printf("twenty-");break;
    case 30:
        printf("thirty-");break;
    case 40:
        printf("forty-");break;
    case 50:
        printf("fifty-");break;
    case 60:
        printf("sixty-");break;
    case 70:
        printf("seventy-");break;
    case 80:
        printf("eighty-");break;
    case 90:
        printf("ninety-");break;
    }

    switch (digits % 10) {
    case 1:
        printf("one.");break;
    case 2:
        printf("two.");break;
    case 3:
        printf("three.");break;
    case 4:
        printf("four.");break;
    case 5:
        printf("five."); break;
    case 6:
        printf("six.");break;
    case 7:
        printf("seven.");break;
    case 8:
        printf("eight.");break;
    case 9:
        printf("nine.");break;
    }
    return 0;