Question

Function name : contains_substring

Parameters : string (string), substring (string)

Returns: bool

Description : If the substring is entirely contained within the string, then return True, otherwise return False. An empty substring will always return False. The substring may be longer than the string. You are not allowed to just write “if substring in string”.

Answer 1

Solution:

#include<stdio.h>
#include<math.h>
#include<limits.h>
#include <stdbool.h>
#include<stdlib.h>
#include<stddef.h>

#define size sizeof(int)*100

//Prototype declaration..
bool contains_substring(char *string, char *substring);
int findLength(char *str);

int main( void )
{  
   char *string = NULL;       //String
   char *substring = NULL;       //Substring..
   //Dynamic Memory allocation..
   string = (char *) malloc (size * sizeof (char));
   substring = (char *) malloc (size * sizeof (char));
  
   printf(" Enter the string : ");
   fgets(string, size, stdin);   //Read string 1...
   printf(" Enter the sub-string : ");
   fgets(substring, size, stdin);   //Read substring..
  
   //Func call to find the substring..
   if(contains_substring(string, substring)) {
       printf(" Substring found..!! ");
   }
   else{
       printf(" Substring not found..!! ");
   }
   free(string);                  //Freeing the memory
   free(substring);
return 0;
}
          
/**
* Function to find the substring in a strings..
* Returns the true/fasle of type boolean..
*/
bool contains_substring(char *string, char *substring)
{
   int i = 0;
   int j = 0;
   int count =0;       //Counts the length of continuos mnatching chars

   int stringLength = findLength(string);   //Find & Stores Lenght of String1
   int substringLength = findLength(substring); //Find & Stores Lenght of String2
  
   if(stringLength < substringLength)          //If string2 > string1  
       return false;

   //Travesing the string1 char by char and finding the substring..
   for (i = 0; *(string + i) != '' ; i++) {  

       if(*(string + i) == *(substring + j)) {
           count++;
           j++;
       }
       else {
           i -= count;       //Make 'i' to point the previous position
           count = 0;       //If not equal start from first..
           j = 0;
       }
       if (substringLength == count ) { //Sub string present if equals..
           return true;   //Checking the length for match..      
       }
   }
   return false;       //Return false if substring not found..
}

/**
* Function to find the length of the strings..
* Returns the length of type int..
*/
int findLength(char *string)
{
   int length= 0;
  
   while(*(string+ length) != '') {
       length++;
   }
   length--;   //Omits last null char..
return length;
}

Code Screenshots:

Sample Output:

Following shows how the program works..

                

Output:

                     

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