/* Homework 3 problem 2
 * This program finds the first occurence of a substring in a user defined string
 * Reports the location (0 being the first position) and exits OR reports the absence
*/
#include <stdio.h>

int main( int argc, char** argv )
{

  // Define character arrays 
  // 1024 is the maximum size of the string, it could have been chosen differently
  char S1[1024];
  char S2[1024];
  
  

  // Promt user
  printf("Please enter the original string\n");
  fgets(S1,1024,stdin);
  printf("Please enter the sub-string to be searched\n");
  fgets(S2,1024,stdin);

  // During your testing it is always good to know what is the received from user
  //printf("Original string entered: %s",S1);
  //printf("Substring entered: %s",S2);
  
  
  int i,j=0,location=0;

  for(i=0;S1[i]!='\n';i++){
  
    // if statement is true if there is a match 
    if(S1[i]==S2[j]){
      // Remember this location if j is zero, it is the initial character of substring
      if(j==0){
	location = i;
      }
      // Advance to the next character on the substring
      j++;
      
      // If the termination  character ('\n') on substring is reached
      // Print location and exit
      if(S2[j]=='\n'){
	printf("Substring is found at location %d\n",location);
	exit(0);
      }

    }
    else{
      // No match between current position of substring and current position of original string
      // Return to the first character of substring to compare for next iterations
      j=0; 
    }
  }
    
 
  // If this line is reached, the program did not exit which so the substring is not found
  printf("Substring is NOT found\n");
 
  exit(0);
}