A CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart) is a test to determine whether the user is human or not.
So, the task is to generate unique CAPTCHA every time and to tell whether the user is human or not by asking user to enter the same CAPTCHA as generated automatically and checking the user input with the generated CAPTCHA.
CAPTCHA: x9Pm72se Input: x9Pm62es Output: CAPTCHA Not Matched CAPTCHA: cF3yl9T4 Input: cF3yl9T4 Output: CAPTCHA Matched
The set of characters to generate CAPTCHA are stored in a character array chrs which contains (a-z, A-Z, 0-9), therefore size of chrs is 62.
To generate a unique CAPTCHA every time, a random number is generated using rand() function (rand()%62) which generates a random number between 0 to 61 and the generated random number is taken as index to the character array chrs thus generates a new character of captcha and this loop runs n (length of CAPTCHA) times to generate CAPTCHA of given length.
CAPTCHA: cF3yl9T4 Enter CAPTCHA: cF3yl9T4 CAPTCHA Matched
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