UpCase for *string in C

Question

i wanted to know why i can't transform all my letter into lowercase in my string in my function. I try to print the string before the "if" and it worked so i dont understand why i cannot do :

string[i] = string[i] - 'A' + 'a';

Here my function :

bool is_string_in_array(char * strings[], int n, char * string) {


for (int i=0;i<strlen(string);i++) {
        printf("%c\n",string[i]);
    if (string[i] >= 'A' && string[i] <= 'Z') {
        string[i] = string[i] - 'A' + 'a';

    }
}
for (int i = 0; i < n; i++) {
    if (strcmp(strings[i], string) == 0){
        return true;
    }
}
return false;

}

And i can not use tolower() function ... and i called with :

char *test ={"DOG"};
is_string_in_array(banned_words,n,test);

Thank you for your time

Your code seems to work for me. What problem are you experiencing? — Fred Larson, Jan 03 '19 at 21:53
Post how `low_case_string()` is called. If you are doing something like `low_case_string("Bellahsen Raphael")`, the problem is that code is attempting to modify a _string literal_ which is _undefined behavior_ (UB). Post a [mcve] to save us all time. — chux - Reinstate Monica, Jan 03 '19 at 21:53
looks like you are printing out the characters before you convert them to uppercase — bruceg, Jan 03 '19 at 21:55
BTW, C has built-in functions `isupper()` and `tolower()`. You don't need to do all that arithmetic. — Barmar, Jan 03 '19 at 22:02
You can always make a copy of the input string with the `strdup` function, and check that one. Just make sure to free the memory before you return. — bruceg, Jan 03 '19 at 22:07
@Barmar And not only that, those built-in functions are portable while the arithmetic is not. There is no guarantee of order for alphabetical characters. — Christian Gibbons, Jan 03 '19 at 23:40
And finally there's `stricmp()`, which compares two strings case-insensitively, so you don't need to update the string. — Barmar, Jan 04 '19 at 00:39

score 1 · Answer 1 · answered Jan 03 '19 at 22:01

#include <stdio.h>
#include <stdlib.h>
void low_case_string(char * string);
int main()
{
    char str[]="TESTING";
    low_case_string(str);
    return 0;
}
void low_case_string(char * string)
{

    for (int i=0; i<strlen(string); i++)
    {
        if (string[i] >= 'A' && string[i] <= 'Z')
        {
            string[i] = string[i] - 'A' + 'a';

        }
    printf("%c\n",string[i]);
    }
}

It does work the way you have writen your code, but you printed out the result before there would have been any change. I am not sure if this is what you were asked for

UpCase for *string in C

1 Answers1