对于迭代，使用C ++对“编程原理和实践”进行“尝试此练习”练习

Question

I'm studying in this book (self study) and I'd really appreciate if you could help me with a little 'try this' exercise.

This is the code I wrote:

#include "../../../std_lib_facilities.h"

int main()
{
    for (char i ='a'; i <='z'; ++i) {
        int x = i;
        cout << i << '\t' << x << '\n';
    }
    keep_window_open();
    return 0;
}

The next step, according to the book, is: "[...] then modify your program to also write out a table of the integer values for uppercase letters and digits" Is there a function to do that, or do I simply have to repeat the loop starting from A? Thanks

Answer 1

Yes, repeat the loop from 'A' to 'Z' and '0' to '9'.

Assuming your book has covered functions (which it may not have), you might refactor your for loop into its own function perhaps called displayCharactersInTable which takes as arguments the first character and last character. Those would replace the use of 'a' and 'z' in the loop. Thus your main function would look like:

...
displayCharactersInTable('a', 'z');
displayCharactersInTable('A', 'Z');
displayCharactersInTable('0', '9');
...

Answer 2

const char lc_alphabet[] = "abcdefghijklmnopqrstuvwxyz";
const char uc_alphabet[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

int main() {
    for (const char *cur = lc_alphabet; cur < lc_alphabet + sizeof(lc_alphabet); ++cur)
        std::cout << *cur << \t << (int)*cur << '\n';
    for (const char *cur = uc_alphabet; cur < uc_alphabet + sizeof(uc_alphabet); ++cur)
        std::cout << *cur << \t << (int)*cur << '\n';
return 0;
}

This code does not assume that character representations are contiguous (or even increasing alphabetically), so it will work for all character encodings.

Answer 3

int b = 97; // the corresponding decimal ascii code for 'a'
int a = 65; // the corresponding decimal ascii code for 'A'

for(int i = 0; i < 26; ++i)
    cout << char('A' + i) << '\t' << a << '\t' << char('a' + i) << '\t' << b << '\n'; //print out 'A' and add i, print out a, print out 'a' and add i, print out b
    ++a; //increment a by 1
    ++b; //increment b by 1