size_t strspn(const char *str1
const char *str2
Finds the first sequence of characters in the string str1
that contains any character specified in str2.
Returns the length of this first sequence of characters found
that match with str2.
The output should be: The number length is 4.
char string="7803 Elm St.";
printf("The number length is %d.\n",strspn(string,"1234567890"));