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2.9. Operators for Characters

Interestingly, the same mathematical operations that work on integers also work on characters. For example, observe the following output.

This program performs character addition. It works by converting the character ‘a’ to ASCII, adding 1 to this value, then converting the result from ASCIIs back to a character.

#include <iostream> using namespace std; int main () { char letter; letter = 'a' + 1; cout << letter << endl; }

Although it is syntactically legal to multiply characters, it is almost never useful to do it.

Earlier I said that you can only assign integer values to integer variables and character values to character variables, but that is not completely true. In some cases, C++ converts automatically between types. For example, the following is legal.

This program performs automatic type converstion. It converts ‘a’ to its ASCII value.

#include <iostream> using namespace std; int main () { int number; number = 'a'; cout << number << endl; }

The result is 97, which is the number that is used internally by C++ to represent the letter ’a’. However, it is generally a good idea to treat characters as characters, and integers as integers, and only convert from one to the other if there is a good reason.

Note

Characters in C++ hold ASCII values, which range from 0 to 128. Uppercase ‘A’ has an ASCII value of 65, lowercase ‘a’ has a value of 97, and a space has a value of 32. C++ converts characters to their ASCII values to perform automatic type conversion and character arithmetic.

Automatic type conversion is an example of a common problem in designing a programming language, which is that there is a conflict between formalism, which is the requirement that formal languages should have simple rules with few exceptions, and convenience, which is the requirement that programming languages be easy to use in practice.

More often than not, convenience wins, which is usually good for expert programmers, who are spared from rigorous but unwieldy formalism, but bad for beginning programmers, who are often baffled by the complexity of the rules and the number of exceptions. In this book I have tried to simplify things by emphasizing the rules and omitting many of the exceptions.

Construct a main function that uses character operations to generate the output ‘r’.

        int main () {
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 char r;
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 int r; #distractor
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 r = 'p' + 2;
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 r = p + 2; #distractor
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 r = 'p' + 3; #distractor
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 cout << r;
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 cout << "r"; #distractor
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}
        

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