Is there a way I can shorten this if statment? - c

Question

I have this really large if statement and it does not look pleasing to the eye as well as not being as efficient as possible.
I'm making a program that (depending on the users input) runs a certain block of code, for example if the user inputs 'a' the program runs a code that adds something to a file etc. By the way this is in a do-while statement(I don't know if this is relevant though).
else if(ansr != 'a' && ansr != 'A' && ansr != 'r' && ansr != 'R' && ansr != 's' && ansr != 'S' && ansr != 'e' && ansr != 'E')
{
printf("Invalid input!\n");
}
As you can see this is a really long if statement and I would like it to be shorter. Thank you

Answer 1

Um, what an example, whatever.
Why don't you use strchr? strchr returns the pointer to a character in a string (if found), NULL otherwise.
else if (strchr("aArRsSeE", ansr) == NULL)
{
printf("Invalid input!\n");
}

Answer 2

I would go with:
switch(tolower(ansr)) {
case 'a':
case 'r':
case 's':
case 'e':
do_stuff();
break;
/* other cases here */
}
Or you can use more library functions such as:
if (strchr("ares", tolower(ansr)) {
do_stuff();
}
strchr function is searching for a given character in the given string and returns NULL if it is not there (or pointer to first occurrence of it, but it is not the use-case which we are interested in here)
This is assuming ansr is in the range of unsigned char or EOF. Otherwise the behavior of tolower is undefined.

Answer 3

To answer your question, I would personally use a switch statement. It is easy to use and easy to read. Another thing which would make your code slightly more readable is using toupper.
Here is an example:
#include <stdio.h>
#include <ctype.h>
int main ()
{
char inp = 'i';
char ansr = toupper(inp);
switch(ansr) {
case 'A' :
// Do something
break;
case 'R' :
// Do something
break;
case 'S' :
// Do something
break;
case 'E' :
// Do something
break;
default :
printf("Invalid input!\n");
}
return 0;
}

Answer 4

It looks like you're trying to write an else if case to catch input characters that you do not support. The else case is perfect for that kind of situation:
...
char input;
//get your input
if (input == 'A' || input == 'a')
DoA();
else if (input == 'R' || input == 'r')
DoR();
else if (input == 'S' || input == 's')
DoS();
else if (input == 'E' || input == 'e')
DoE();
else
DoInvalidInput();
Or if you use tolower() you can put that in a switch statement:
char lowerChar = tolower((unsigned char)input);
switch (lowerChar)
{
case 'a': DoA(); break;
case 'r': DoR(); break;
case 's': DoS(); break;
case 'e': DoE(); break;
default: DoInvalidInput(); break;
}

Answer 5

Depending on if the case of the ansr is important, converting to lowercase before the if statement would half the amount of checks needed.