Generating Pseudo Random Number/Capital Letter

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Hello everyone,

In my program I have to generate a random number/capital letter and cast it as a char.
Online I was able to locate an algorithm that does nearly that:

C++

int main() {
        srand((unsigned) time(NULL));
        
        const int passLen = 10;
        for (int i = 0; i < passLen; i++) {
                cout << (char) (rand() % ('z' - '0' + 1) + '0');
        }
}

My problem is, I don't completely understand how this method works, and because of this I'm not sure how to modify the function to get it to do what I want. Could anyone please explain approximately how this process works so that I can learn to modify this function to my liking?

Thank you, sorry for the fairly basic question. I'm still pretty new to this.

Posted 5-Nov-12 8:01am

Parwarrior7

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OriginalGriff · Accepted Answer · 2012-11-05T08:27:00

OK - look at it in parts:

C++

srand((unsigned) time(NULL));

Initialises a random number generator.

C++

const int passLen = 10;
for (int i = 0; i < passLen; i++) {

Makes the code generate 10 characters

C++

cout << (char) (rand() % ('z' - '0' + 1) + '0');

Does teh actual work.
The cout stuff I assume you understand.
rand() generates a new random number.
% Modulus operator - effectively limits the random number to between zero and the second parameter minus one.
'z' - '0' + 1 The second parameter, sets upper limit of the range of characters.
+ '0' Converts the result to a printable ASCII character - it the random number is 0, then '0', if it is one, the '1', if it is nine then '9', if it is ten then ':' - see here http://www.asciitable.com/[^] for the Ascii characters and you will see what I mean.

The second parameter is just saying "I want my results to be between '0' and 'z', so give me value that is the difference plus one" - because the one will be discarded by the modulus operation. if it was '0' to '9' then it would be 57 - 48 + 1 which is (obviously) 10 - so teh random number would be 0 to 9 inclusive.