So I am completely lost on what to do. I have two strings, one is longer than the other. If the second string is longer than the first string then I have to resize the first array and replace it with the longer substring. I can't use vectors. Please help, I'm so lost and I've been working on this assignment for weeks
Can you use strings? Probably not since with strings it is trivial:
if(s2.size() > s1.size()) s1 = s2;
or, if you're supposed to replace the first with the second in any case, not just when the second is larger, s1 = s2;
and if you can't use strings, it's worth explaining exactly what "I have two strings," means. Are they char arrays instead? Are they static, stack-allocated, or heap-allocated? Existing work-in-progress code would help get an answer relevant to your needs.
@ljzshuai there are more calls to new[] than calls to delete[] in your code