在C ++中通过char访问数组

Question

Usually, I access an array in C++ by the syntax foo[2] , where 2 is the index of an array.

In the below code. I didn't understand how this code is giving output and access this array by index 'b' , 'c' . I am confused it is array index or something else.

int count[256] = {0};
count['b'] = 2;
cout << count['b'] << endl; //output 2
cout << count['c'] << endl; //output 0

Output

2
0

Answer 1

Type char is actually an integral type. Every char value represented by a character literal has an underlying integral value it corresponds to in a given code page, which is probably an ASCII table . When you do:

count['b'] = 2;

you actually do:

count[98] = 2;

as character 'b' corresponds to an integral value of 98 , character 'c' corresponds to an integral value of 99 and so on. To illustrate, the following statement:

char c = 'b';

is equivalent of:

char c = 98;

Here c has the same underlying value, it's the representation that differs.

Answer 2

Remember that in c++ characters are represented as numbers. Take a look at this ascii table. http://www.asciitable.com

According to this the character 'b' is represented 98 and 'c' as 99. Therefore what your program is really saying is...

int count[256] = {0};
count[98] = 2;
cout << count[98] << endl; //output 2
cout << count[99] << endl; //output 0

Also incase you don't know saying an array = {0} means zero initialize every value so that is why count['c'] = 0 .

In C/C++ there is not 8 bit / 1 byte integer. We simply use the char type to represent a single (signed or unsigned) byte and you can even put signed and unsigned infront of the char type. Char really is just another int type which we happen to use to express characters. You can also do the following.

char b = 98;
char c = 99;
char diff = c - b; //diff is now 1

Answer 3

Because characters are always represented by integers in the computer, it can be used as array indices.

You can verify by this:

char ch = 'b';
count[ch] = 2;
int i = ch;
cout << i << endl;
cout << count[i] << endl;

Usually the output is 98 2 , but the first number may vary depending on the encoding of your environment.