Question

My goal is to call a function and the function will return me 0 / 1 if the sent string has the
sent substring in it , I do not need to find its index
for example:

String : “Hello World”
SubString : “rl”
will return 1

String : “asssbdsd”
SubString : “ab”
will return 0

so I’ve come up with this solution :

int HasSubstr(char* mainStr, char* subStr)
{
    if (!*subStr)
    {
        return 1;
    }
    if (!*mainStr)
    {
        return 0;
    }
    if (*mainStr == *subStr)
    {
        return HasSubStr(mainStr + 1, subStr + 1);
    }
    else
    {
        while(*(subStr -1))
        {
            subStr--;
        }
        return HasSubStr(mainStr + 1, subStr);
    }
}

but it’s not a pure recursion and i need it to be a pure recursion
, help would be much applied

Yes this is homework

Answer 1

Don’t try to fit it all within one function.

int StartsWith(const char *mainstr,const char *subStr)
{
  if (*subStr == '\0') return 1;
  if (*mainStr != *subStr) return 0;
  return StartsWith(mainStr+1,subStr+1);
}

int HasSubstr(const char *mainStr,const char *subStr)
{
  if (StartsWith(mainStr,subStr)) return 1;
  if (*mainStr == '\0') return 0;
  return HasSubstr(mainStr+1,subStr);
}