How to change function arguments in C?

Question

Inside a C function I am basically trying to convert all the values of the func argument into uppercase. Then use that argument somewhere else in the function. I don't want to change the variable passed into the function. Just the argument locally. Argument is an array of chars.

Here is what I tried:

int calculate_score(char *word[])
{
    for (int i = 0, n = strlen(word); i < n; i++)
    {
     if (islower(word[i]) != 0)
     {
        //this piece of code is not working
         toupper(word[i]);
     }
    } 

How do I achieve this ?

EDIT: I have included all the necessary header files string and ctype for this to work

Answer 1

If you do not want to change the argument string, you should make a copy for local use:

• if there is a reasonable maximum length for this string, you can use a local array of char ;
• otherwise you can allocate memory for the copy and
• use a loop to convert the contents to upper case
• and free this copy before returning (if it was allocated)

Note that the argument should not be char *word[], but char *word or better const char *word.

Here is an example:

#include <errno.h>
#include <stdlib.h>
#include <string.h>

int calculate_score(const char *word) {
    int res = 0;
    size_t i, n = strlen(word);
    char *copy = malloc(n + 1);
    if (copy == NULL) {
        fprintf(stderr, "calculate_score: allocation error\n");
        return -1;
    }
    for (i = 0; i < n; i++) {
        unsigned char c = word[i];
        copy[i] = (char)toupper(c);
    }
    copy[i] = '\0';
    // use copy for the computation
    [...]
    free(copy);
    return res;
}

Answer 2

If you don't want to change the string passed into your function, make a copy of it and work on that.

void foo(char *bar) {
    char *s = strdup(bar);

    // do something to s
    // bar remains unchanged

    // don't forget to free that memory.
    free(s);
}