How to compare more than 2 strings in C?

Question

I know there is the strcmp but it just let me compare two strings, And I need to compare a lot of them

This one doesn't work:

if(strcmp (resposta, "S" || "s" || "N" || "n")== 0)
        printf("Resposta = S");
    else
        printf("Resposta != S");

    printf("\nfim");

Answer 1

Your method isn't working as you expected because the expression "S" || "s" || "N" || "n" is the same as "S" because of short circuit.

You have to compare it with the candidate strings one by one:

if (strcmp(resposta, "S") == 0
    || strcmp(resposta, "s") == 0
    || strcmp(resposta, "N") == 0
    || strcmp(resposta, "n") == 0)
{
    printf("Resposta = S");
}

Answer 2

if( strcmp (resposta, "S") == 0 || strcmp (resposta,"s") == 0  || strcmp (resposta,"N") == 0 || strcmp (resposta, "n") == 0)

Answer 3

The signature of the standard library function strcmp is -

int strcmp(const char *s1, const char *s2);

However, you are calling it as

strcmp(resposta, "S" || "s" || "N" || "n")

The second argument evaluates to 1, which is of type int, because the string literals evaluate to a pointer to its first character and it cannot be NULL. This is clearly wrong. You should replace it by

if(!((strcmp(resposta, "S") && strcmp(resposta, "N") && strcmp(resposta, "n")))
    printf("Resposta = S");
else
    printf("Resposta != S");

Answer 4

If you have a lot of strings to compare against, you could make an array out of them and iterate over it. In this example the array is terminated with a NULL (so the while condition works):

const char *strings[] = { "S", "Sim", "N", "NAO", NULL };
                                              // ^ add more strings here
const char **s = strings;
while (*s) {
    if (strcmp(resposta, *s) == 0) {
        (void) printf("Matched: %s\n", *s);
        break; // stop searching when a match is found (the matching string is *s)
    }
    ++s;
}
if (!*s) {
    (void) printf("Didn't match anything\n");
}

A better way if you have a lot of strings to match against would be to sort the array of strings and do binary search in it.

Answer 5

If you're looking for a string that is only a single char, you can use a switch statement.

switch(*string) //will compare the first character of your string
{
    case('s'):
    {
        //whatever you do
        break;
    }
    case('S'):
    {
        //whatever else
        break;
    }
    ... //other characters
    default:
    {
        //error handling on incorrect input
        break;
    }
}

Edit: If you are comparing strings of different length (i.e. you are looking for a prefix in a string), be aware that strcmp() will never consider them equal.

If you need to find a prefix, you need to strncmp() (note the n) with each string and string length individually.