C语言Matrix编程题——[Pointers and C-String]D. Liang 7.8 Checking substring

[Pointers and C-String]D. Liang 7.8 Checking substring

Description：

Write a function to check whether string s1 is a substring of string s2. The function returns the first index in s2 if there is a match. Otherwise, return -1.
The function header is:

int indexOf(const char *s1, const char *s2)

Hint:

Don’t submit the main() function.

Programme:

//Date:2020/5/14
//Author:Kamenrider Justice
int indexOf(const char *s1, const char *s2)
{
   int index,length1,length2,i,j,flag;
   length1=strlen(s1);
   length2=strlen(s2);
   for(i=0;i<=length2-length1;i++)
   {
      flag=1;
      for(j=0;j<length1;j++)
      {
         if(s1[j]!=s2[i+j])
         {
            flag=0;
            break;
         }
      }
      if(flag)
      {
         index=i;
         return index;
      }
   }
   return -1;
}

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