1. Write a program containing the function str_reverse(s1, s2) that reverses the case of letters in the string s1 and saves the converted string in s2. The function must also return a pointer to s2....

1. Write a program containing the function str_reverse(s1, s2) that reverses the case of letters in the string s1 and saves the converted string in s2. The function must also return a pointer to s2.

2. Write a program that accepts a string from the user and inserts a : as the delimiter after every five characters before printing the delimited string.

3. Write a program containing the function str_replace(s, s1, s2) that replaces the fi rst occurrence of substring s1 with s2 in the string s. The function must return a pointer to s if the replacement is successful, or NULL otherwise. (HINT: Use the strstr function.)