What I want to do is to iterate through the quote till the end of the quote/(*quote has nothing in it). Is my code valid?
char *quote = "To be or not to be, that is the question.";
for (quote = 0; *quote != NULL; quote++){
*quote = tolower(*quote);
}
You probably need another pointer to traverse the array, otherwise access to your original string will be lost.
And preferably only use NULL for pointers.
Don't use 0 as the initial value, unless you want to use indices instead (see below).
Doing char *quote = will simply make quote point to the read-only literal, instead of copying the string. Use char quote[] = instead.
char quote[] = "To be or not to be, that is the question.";
char *quotePtr;
for (quotePtr = quote; *quotePtr != '\0'; quotePtr++){
*quotePtr = tolower(*quotePtr);
}
Test.
Using indices:
char quote[] = "To be or not to be, that is the question.";
int i;
for (i = 0; quote[i] != '\0'; i++){
quote[i] = tolower(quote[i]);
}
Test.
"") is read-only. Trying to modify it would result in undefined behaviour - an error can occur, nothing can happen, it can actually modify the string literal or something worse. If you do char *quote=, you simply make quote point to this read-only string, so the above code would try to modify it. However, if you do char quote[]=, this would actually create a copy of the string literal and make quote point to the copy, which you are free to modify.Consider this as an expansion to the answer given by Dukeling
When you use
char *quote = "Hello World";
This makes a read-only string, means that you can't change its contents in a simpler way.
Here *quote points to 'H'
BUT, you cannot do *quote = 'A';
This will give you an error.
If you wish to make changes to the characters in a string, it is a good habit to use arrays.
char quote[] = "Hello World";
Here also *quote points to 'H'
BUT, in this case *quote = 'A' is perfectly valid.
The array quote will get changed.
You're reassigning quote in your for initializer, which is invalid and will cause an access-violation because you're dereferencing it in the *quote != NULL part.
Semantically NULL and '\0' are equivalent, but syntactically I'd prefer this. Note that by using this approach you keep a pointer to (the start of) the string.
wchar const_t* quote = L"To be or not to be, that is the question.";
for( wchar_t* c = quote; *c != '\0'; c++ ) {
*c = tolower( *c );
}
alternatively using an index:
wchar const_t quote[] = L"To be or not to be, that is the question.";
for( size_t i = 0; i < sizeof(quote); i++ ) {
quote[i] = tolower( quote[i] );
}
(note that the semantics of sizeof will change if the value of quote is not known at compile time)
wchar const_t* quote is a constant string literal which you cannot modify so your code will fail.
quote = 0is incorrect.unsigned int?