Question

****Using c++

(Check Substrings) Write the following 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.

int indexOf(const string& s1, const string& s2)

Write a test program that reads two strings and checks whether the first string is a substring of the second string.

Answer 1

Answer:

#include<stdio.h>
#include<string.h>
int main()
{
   const char substring[]="cd";//declaring string constant what we need to search
   const char string[]="abcdefgh";//declaring a text where we need to search
   int len1,len2,i,j,flag,ind=-1;
   len1=strlen(substring);//finding the length of the searching string
   len2=strlen(string);//finding the length of the textstring
   flag=1;
   for(i=0;i<=(len2-len1);i++)//These are the possiblities that the string may present
   {
       flag=1;
       for(j=i;j<(i+len1);j++)//we need to check length of the substring everytime
       {
           if(string[j]!=substring[j-i])//checking each character of substring is present in the string everytime
           {
               flag=0;
               break;  
           }
           ind=i;  
       }
       if(flag==1)
           break;  
   }
   if(flag==1)//if the string is present in text
       {
           printf("Search successful at index %d",ind);
       }
   else
       printf("Search unsuccessful");//string is not present in the text
   return 0;
}

output:

IF you have any doubts..please comment..Thank you..