Is it ok to compare symbols with each other?

    #include <iostream>
using namespace std;// For Example, Why if "k = 4" it outputs "r o" ? //
int main() {
    char word[] = "programming";
    int k;
    cin >> k;
    for (int i = 0; i < k; i  )
        if (word[i] > word[i   1]) {
            cout << word[i] << endl;
        }
}

CodePudding user response：

Is it ok to compare symbols with each other?

Yes, it is OK.

Why if "k = 4" it outputs "r o" ?

Character types are integers. Each integer value of the character type is mapped to a symbol¹. This mapping is called a character set or character encoding.

In the character encoding of the system where you ran the program, the value of the character that maps to the symbol 'r' has a greater value than the character that maps to the symbol 'o', while that 'o' character has smaller value than the character that maps to 'g'.

¹ This is a simplification. There are special non-printable charcters such as null terminator which aren't symbols as such. Furthermore, the mapping isn't so simple in case of variable length encodings (Unicode).

CodePudding user response：

The char data type is an integral type, meaning the underlying value is stored as an integer. Moreover, the integer stored by a char variable is intepreted as an ASCII character.

ASCII specifies a way to map english characters(and some other few symbols) to numbers between 0 and 127. That is, each english character(and some other few symbols) has a corresponding number between 0 and 127. This number is formally called a code point.

For example, the code point for the english character a is 97. Similarly, the code point for the english character H is 72. You can find the list of code points for all the characters here.

The important thing to note here is that the underlying value of a char variable is stored as an integer. Lets take some examples to clarify this,

char var1 = 'a'; //here var1 is stored as the integer 97 
char var2 = 'H'; //here var2 is stored as the integer 72

In the above snippet, var1 is stored as the integer 97 because the code point for the english character a is 97. Similarly, var2 is stored as the integer 72 because the english character H corresponds to the code point 72.

Now lets come back to your original question. In particular what happens when k =4.

For k = 4, the for loop will be executed 4 times.

Iteration 0: Here i = 0

The if block basically translates to:

if (word[0] > word[0   1]) {
            cout << word[0] << endl;
        }

which is:

if ('p' > 'r') {
            cout << 'p' << endl;
        }

which is(using the ascii table):

if (112 > 114) {
            cout << 'p' << endl;
        }

since the condition inside if is false, the body of the if block will not be executed and you'll get no output.

Iteration 1: Here i = 1

The if block basically translates to:

if (word[1] > word[1   1]) {
            cout << word[1] << endl;
        }

which is:

if ('r' > 'o') {
            cout << 'r' << endl;
        }

which is(using the ascii table):

if (114 > 111) {
            cout << 'r' << endl;
        }

since the condition inside if is true, the body of the if block will be executed and you'll get r as output(which is followed by a newline).

Iteration 2: Here i = 2

The if block basically translates to:

if (word[2] > word[2   1]) {
            cout << word[2] << endl;
        }

which is:

if ('o' > 'g') {
            cout << 'o' << endl;
        }

which is(using the ascii table):

if (111 > 103) {
            cout << 'o' << endl;
        }

since the condition inside if is true, the body of the if block will be executed and you'll get o as output(which is followed by a newline).

Iteration 3: Here i = 3

The if block basically translates to:

if (word[3] > word[3   1]) {
            cout << word[3] << endl;
        }

which is:

if ('g' > 'r') {
            cout << 'g' << endl;
        }

which is(using the ascii table):

if (103 > 114) {
            cout << 'g' << endl;
        }

since the condition inside if is false, the body of the if block will not be executed and you'll get no output.

Hence you get the output:

r
o