Replacing String elements in C

Question

I am trying to replace asterisk to some words in a string. e.g: if the string is 'A big giant person scared me', and i need the words 'giant' and 'scared' to be replaced with asterisk. the string should be 'A big ***** person ****** me'

here is my code

int lengthString(char* str) {
    int i = 0;
    while (str[i] != '\0')
            i++;
    return i;
}

void replace(char* start, int length, char ch) {
     for (int i = 0; i < length; i++)
            start[i] = ch;
}

void redact(char* toRedact, char** dictonary, int dicSize) {
    for (int i = 0; i < dicSize; i++) {
            char* redact = dictonary[i];
            char* lastPos = toRedact;
            char* nextPos = strstr(lastPos, redact);
            while (lastPos != NULL) {
                    if (nextPos == NULL){
                      break;
                    }
                    replace(nextPos, lengthString(redact), '*');
                    lastPos = nextPos + 1;
            }
    }
}

int main() {

   char* test[4];
   char* dictionary[4];
   dictionary[0] = "big";
   dictionary[1] = "giant";
   dictionary[2] = "scared";
   dictionary[3] = "person";

   test[0] = "A giant scared me";
   test[1] = "A big scared me";
   test[2] = "A person scared me";

   for(int i = 0; i < 3; i++) {
     redact(test[i], dictionary, 4);
     printf("%s\n", test[i]);
   }

   return 0;
 }

output: seg fualt

You have pointers to string literals. All string literals in C are *read only*. Attempting to modify them leads to *undefined behavior*. — Some programmer dude, May 03 '18 at 12:29
You're attempting to modify a **string constant**. They are read-only in C. — , May 03 '18 at 12:29
You should create new strings. char * is allocated in read-only memory and can't be modified. — Rez Trentnor, May 03 '18 at 13:54
"*char * is allocated in read-only memory and can't be modified.*" <- what? — , May 03 '18 at 15:35

Replacing String elements in C

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