For this question you will write code for the following function:

char$*$ onlyDigits$($char $*$str$)$

This function returns a dynamically created new string which contains only the digits from the

given string. Some examples:

onlyDigits$((210)555-1337)$ should return a new string $2105551337.$

onlyDigits$($pi $=3\mathrm{.}14159...)$ should return a new string $314159.$

onlyDigits$($HelloW orld$)$ should return a new string $.$

Some additional requirements for your onlyDigits function:

$$ The new string should have exactly enough size to store the digits in the string and a null

terminator $($i$.$e$.,$ don$$t malloc more memory than you need$).$ Remember that $\backslash 0$ is the null

terminator character which ends a string.

$$ If your malloc fails $($i$.$e$.$ it returns N U LL$),$ your function should call exit$(-1).$

$$ The only functions your onlyDigits implementation should call are numDigits, malloc, sizeof $,$

exit, and strlen.

$($a$)(0$ points$)$ Complete the following helper function which returns the number of digits in the

given string. This should be a useful function when writing onlyDigits.

Solution:

$//$Return the number of digits in the given string

int numDigits$($ char $*$str $)$

$\{$

int i $=0$;

int count $=0$;

int size $=$ strlen$($ str $)$;

for$($ i$=0$; i$=0$ && str$[$i$]<=9)$

count$++$;

$\}$

return count;

$\}$