Using toupper for first character in the vector string - c++

Question

How to use toupper() to convert the first letter to uppercase of each element inside a vector of strings?
This is what I've tried...
string word;
vector<string> text;
while(cin >> word){
text.push_back(word);
}
for(decltype(text.size()) i = 0; i != text.size()) {
text[0] = toupper(text);
}

Answer 1

You can simply do this,
string word;
vector<string> text;
while(cin >> word){
word[0] = static_cast<char>(toupper(static_cast<int>(word[0])));;
text.push_back(word);
}
Now you don't have to iterate through the word list to change the first letter of every entry to upper.

Answer 2

for(auto& s : text)
if (!s.empty()) s[0] = std::toupper(s[0]);
Or more fancy:
std::transform(std::istream_iterator<std::string>{std::cin}, {},
std::back_inserter(text),
[](auto s) {
if (!s.empty()) s[0] = std::toupper(s[0]);
return s;
});

Answer 3

There are a couple of problems with your code.
Your 2nd loop runs endlessly, you need to add ++i to the end of the loop to actually iterate each string in the vector and terminate the loop when the end of the vector is reached:
for(decltype(text.size()) i = 0; i != text.size(); ++i)
On a side note, you can replace decltype(text.size()) with vector<string>::size_type instead, or decltype(text)::size_type.
A range-based for loop would avoid both issues:
for(string &str : text)
Regarding your actual error, this line does not compile:
text[0] = toupper(text);
Because toupper() takes a single character as input, but you are passing it the vector itself, rather than a single character from a single string in the vector. You would have needed to do this instead:
text[i][0] = toupper(text[i][0]);
However, you actually need to convert characters to unsigned char when passing them to toupper(), eg (I'm separating each step so you can see it more clearly):
string &str = text[i];
char ch = str[0];
unsigned char uc = static_cast<unsigned char>(ch);
uc = toupper(uc);
ch = static_cast<char>(uc);
str[0] = ch;
text[i] = str;
Which, obviously, can also be written as a string expression, if you want:
text[i][0] = static_cast<char>(
toupper(
static_cast<unsigned char>(
text[i][0]
)
)
);
The reason why the cast is needed is explained on this reference page:
Parameters
ch - character to be converted. **If the value of ch is not representable as unsigned char and does not equal EOF, the behavior is undefined.
...
Like all other functions from <cctype>, the behavior of std::toupper is undefined if the argument's value is neither representable as unsigned char nor equal to EOF. To use these functions safely with plain chars (or signed chars), the argument should first be converted to unsigned char