How can I make switch-case statements case insensitive?

Question

How can I make a switch-case statement to not be case sensitive? Say I made something like this:

#include <stdio.h>

char choice;
int main ()
{
char choice;
printf("Will you choose A,B, or C?\n>");
scanf(" %c", &choice);

switch(choice)
{
    case 'A': 
         printf("The First Letter of the Alphabet");
         break;
    case 'B':
         printf("The Second Letter of the Alphabet");
         break;
    case 'C':
         printf("The Third Letter of the Alphabet");
         break;
}
}

It would only respond to capital letters. How do I make it respond to lower case letters?

Lowercase/uppercase your choice. – Tymoteusz Paul Oct 13 '14 at 15:27 — Tymoteusz Paul, Oct 13 '14 at 15:27

score 32 · Answer 1 · answered Oct 13 '14 at 15:27

32

toupper in <ctype.h> converts a character to uppercase:

#include <stdio.h>
#include <ctype.h>

char choice;
int main ()
{
printf("Will you choose A,B, or C?\n>");
scanf(" %c", &choice);

switch(toupper(choice))  // Changed line
{
    case 'A': 
         printf("The First Letter of the Alphabet");
         break;
    case 'B':
         printf("The Second Letter of the Alphabet");
         break;
    case 'C':
         printf("The Third Letter of the Alphabet");
         break;
}

answered Oct 13 '14 at 15:27

Klas Lindbäck

33,105
5
57
82

1

I actually prefer this method. Seems more elegant and less error prone. Especially in this case where you are looking at case-insensitivising specifically. – JoErNanO Oct 13 '14 at 17:12
2

@JoErNanO, in the general case yes, but it's also good to understand that the case construct can take several `case` after each other. I like both answers. If you user `toupper()`, you need to be aware of the limitations and quirks of runtime, if applicable. http://stackoverflow.com/questions/12493496/c-c-utf-8-upper-lower-case-conversions If you use several `case`, you need to be aware of the limitations of the compiler. It might only accept ASCII, for instance. Trade-offs. :) – Prof. Falken Oct 13 '14 at 17:40
@Prof. Falken I absolutely agree. – JoErNanO Oct 15 '14 at 22:24

score 14 · Accepted Answer · answered Oct 13 '14 at 15:27

14

You simply need this :-

switch(choice)
{
case 'A': 
case 'a':
     printf("The First Letter of the Alphabet");
     break;
case 'B':
case 'b':
     printf("The Second Letter of the Alphabet");
     break;
case 'C':
case 'c':
     printf("The Third Letter of the Alphabet");
     break;
}

and so on to continue your series.

Actually,what it does is that it bypasses(skims) upto bottom until it finds the first break statement matching the case thereby executing all the cases encountered in between!!!

answered Oct 13 '14 at 15:27

Am_I_Helpful

18,735
7
49
73

2

I was going to write that but my touchpad (Lenovo) is evil. Very very evilly broken. You won. :) +1 – Prof. Falken Oct 13 '14 at 15:28
Thank You very much. My C learning book said nothing of this before moving onto the next choice method. – Jeremy Oct 13 '14 at 15:28
@Prof.Falken-Professor.,same here! But,I don't know how I won the race. Ha-ha-ha... – Am_I_Helpful Oct 13 '14 at 15:29
1

Lenovo B590? @Jeremy, click the little accept check, the green, next to this answer. – Prof. Falken Oct 13 '14 at 15:32
May I know the reason for downvoting! – Am_I_Helpful Oct 13 '14 at 15:40
1

Well, if you get 10 upvotes or more, someone will likely downvote. Get used to it... – Prof. Falken Oct 13 '14 at 17:35
I dont like this a all. What if I have more than 1 latter switch, then you need to pass all options: AAA, AAa, Aaa, aaa, aaA,... – Gil Epshtain Oct 20 '22 at 07:33
@GilEpshtain - It's fine if you don't like it. But, honestly, I didn't understand your point. Would you like to elaborate, please? – Am_I_Helpful Oct 20 '22 at 11:21
@Am_I_Helpful - In case your switch key isn't a single letter the switch will be: `case SUNDAY: case SUNDAy: case SUNDaY: case SUNDay: ....` This is of course not maintainable – Gil Epshtain Oct 20 '22 at 11:39

score 6 · Answer 3 · answered Oct 13 '14 at 15:27

6

Before the switch(), add:

choice = toupper(choice);

And if you haven't already got it, #include <ctype.h> to get the prototype.

answered Oct 13 '14 at 15:27

JohnH

2,713
12
21

score 1 · Answer 4 · answered Oct 13 '14 at 15:28

You can give 2 cases one by one,

switch(choice)
{
case 'A':
case 'a':
     printf("The First Letter of the Alphabet");
     break;
case 'B':
case 'b':
     printf("The Second Letter of the Alphabet");
     break;
case 'C':
case 'c':
     printf("The Third Letter of the Alphabet");
     break;
}

How can I make switch-case statements case insensitive?

4 Answers4