Classic example of C language - convert the input two digits into English

Write a program , Ask the user to enter a two digit number , Then show the number of English words ：

Enter a two-digit number: 45
You entered the number forty-five.
Tips : Break down a number into two numbers . Use one switch Statement displays the word corresponding to the first digit (“twenty”、"thirty” etc. ), In the second switch Statement displays the word corresponding to the second digit . Don't forget it 10~19 Require special treatment .
 

# include <stdio.h>

int main()
{
	int a1, a2;

	printf("Enter a two-digit number: ");
	scanf("%1d%1d", &a1, &a2);

	// Solve first 10-19  The number of 
	if(a1 < 2){
		switch(a2){
		case 0: printf("You entered the number ten.\n"); break;
		case 1: printf("You entered the number eleven.\n"); break;
		case 2: printf("You entered the number twelve.\n"); break;
		case 3: printf("You entered the number thirteen.\n"); break;
		case 4: printf("You entered the number fourteen.\n"); break;
		case 5: printf("You entered the number fifteen.\n"); break;
		case 6: printf("You entered the number sixteen.\n"); break;
		case 7: printf("You entered the number seventeen.\n"); break;
		case 8: printf("You entered the number eighteen.\n"); break;
		case 9: printf("You entered the number nineteen.\n"); break;
		}
	}
	else{
		// Ten digits 
		switch(a1){
		case 2: printf("You entered the number twenty"); break;
		case 3: printf("You entered the number thirty"); break;
		case 4: printf("You entered the number forty"); break;
		case 5: printf("You entered the number fifty"); break;
		case 6: printf("You entered the number sixty"); break;
		case 7: printf("You entered the number seventy"); break;
		case 8: printf("You entered the number eighty"); break;
		case 9: printf("You entered the number ninety"); break;
		}
		// Single digit 
		switch(a2){
		case 0: printf(".\n"); break;
		case 1: printf("-one.\n"); break;
		case 2: printf("-two.\n"); break;
		case 3: printf("-three.\n"); break;
		case 4: printf("-four.\n"); break;
		case 5: printf("-five.\n"); break;
		case 6: printf("-six.\n"); break;
		case 7: printf("-seven.\n"); break;
		case 8: printf("-eight.\n"); break;
		case 9: printf("-nine.\n"); break;
		}
	}

	return 0;

}