Rabin Carp String Matchin Algorithm In C

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 #include <stdio.h>  
 #include <stdlib.h>  
 #include <string.h>  
 #include <errno.h>  
   
 int found_f=0,found_r=0,pat_val=0;  
   
 int main (){  
   system("clear");  
 while(1){  
   int i,j=0;  
   char pattern[256]={0};  
   char filename[256] = {0};  
   //Get file  
   printf("Enter path of file to read(q to exit): ");  
      if (fgets(filename, sizeof(filename), stdin) == NULL){  
        fprintf(stderr, "Invalid input!\n");  
        exit(-1);  
      }  
   
   filename[strlen(filename) - 1] = '\0';  
   FILE *file = fopen(filename, "r");  
   if(filename[0]=='q'){  
     system("clear");  
     printf("Program Exited!!!\n");  
     exit(0);  
   }  
     if (!file){  
        fprintf(stderr, "Unable to open %s: %s\n",  
        filename, strerror(errno));  
        continue;  
   }  
   //Get file size  
   fseek(file, 0L, SEEK_END);  
   int sz = ftell(file);  
   fseek(file, 0L, SEEK_SET);  
     
   //create file size array  
   char buffer[sz];  
   for(i=0;i<sz;i++){  
     buffer[i]=0;  
   }  
     
   //Get pattern  
   printf("Enter pattern to check : ");  
      if (fgets(pattern, sizeof(pattern), stdin) == NULL){  
        fprintf(stderr, "Invalid input pattern!\n");  
        exit(-1);  
      }  
      pattern[strlen(pattern)-1]='\0';  
      for(i=0;i<strlen(pattern);i++){  
        pat_val=pat_val+pattern[i]; //ascii value of pattern  
      }  
   int ch= 0;  
   printf("\n");  
   //Get char by char from file  
      while ( (ch = fgetc(file)) != EOF ){  
     buffer[j]=ch;  
     j++;  
     find(&buffer,&pattern);  
       
      }  
      if(!found_f){  
     printf("No matching sub string found in forword comparition\n");  
   }  
   if(!found_r){  
     printf("No matching sub string found in reverse comparition\n");  
   }  
   //for(i=0;i<sz;i++){  
   //  printf("%c",buffer[i]);  
   //}  
   found_f=0;  
   found_r=0;  
   pat_val=0;  
   printf("\n");    
      fclose(file);  
  }  
   return 0;  
 }  
   
 int find(char *buffer,char *pattern){  
   int i=0,k=0,l=0;  
   if(strlen(buffer)<strlen(pattern)){  
     return 0;  
   }  
   else{  
     for(i=strlen(buffer)-strlen(pattern);i<strlen(buffer);i++){  
       int key=0;  
       for(k=i;k<(strlen(pattern)+i);k++){  
         key=key+buffer[k]; //ascii value of key  
       }  
       if(key==pat_val){  
         int m=0,n=0;  
         //Forword comparition  
         for(l=0;l<strlen(pattern);l++){  
           if(pattern[l]==buffer[i+l]){  
             n++;  
           }  
           else{  
             break;  
           }  
         }  
         if(n==strlen(pattern)){  
           printf("Matching sub string found in forword signal in %d possition.\n",i+1);  
           found_f=1;  
         }  
         n=0;  
         //Reverse comparition  
         for(l=strlen(pattern)-1;l>=0;l--,m++){  
           if(pattern[l]==buffer[i+m]){  
             n++;  
           }  
           else{  
             break;  
           }  
         }  
         if(n==strlen(pattern)){  
           printf("Matching sub string found in reverse signal in %d possition.\n",i+m);  
           found_r=1;  
         }  
       }  
     }  
   }  
 }