Counting Number Of Digits In C++

We validate phone numbers, Zip code, credit card numbers, etc using number of digits.

How to get the number of digits?

 When we have a number as the  string  then we can find the count by using the ASCII value.
ASCII value of '0' is 48 and '9' is 57. we have to check the ASCII of each character and if it matches the numerical range then we have increase the count.

Following function helps us to count the number of digits

unsigned int CountDigits(LPCTSTR lpTxt)
{
    unsigned int nCount =0;
    for(;*lpTxt!='\0'; lpTxt++)
    {
        if(*lpTxt>=48 && *lpTxt <58)
            nCount++;
    }
    return nCount;
}