for循环C++'toupper'实现

Question

Can someone explain why this short code in C++ doesn't produce the expected output. The code is supposed to print the string in capital letters.

#include <iostream>
#include <string>
using namespace std;

int main(){
    string sample("hi, i like cats and dogs.");
    cout << "small: " << sample << endl << "BIG  : ";

    for(char c: sample)
        cout << toupper(c);
    cout<<endl;

return 0;
}

The output of the above program is:

small: hi, i like cats and dogs.
BIG  : 72734432733276737569326765848332657868326879718346

but I expected:

small: hi, i like cats and dogs.
BIG  : HI, I LIKE CATS AND DOGS.

I've only programmed in python.

Answer 1

toupper returns int . You need to cast the return value to char such that the output stream operator << prints out the character and not its numeric value.

You should also cast the input to unsigned char , to cover the case where char is signed and your character set includes negative numbers (this would invoke undefined behaviour in toupper ). For example,

cout << static_cast<char>(toupper(static_cast<unsigned char>(c)));

Note that you need to include the relevant header ( cctype if you want std::toupper or ctype.h if you want C's toupper .)

Answer 2

It's printing the ASCII values which are integers. I agree with @Captain Obvlious.

Answer 3

#include <iostream>
#include <string>
using namespace std;

int main(){
    string sample("hi, i like cats and dogs.");
    cout << "small: " << sample << endl << "BIG  : ";

    for(char c: sample)
        cout << (char)toupper(c);
    cout<<endl;

return 0;
}

// toupper() return integer value