Segmentation fault in C txt file I/O -

ok guys, purpose of program read text file called orginal.txt containing names in format:

kyle butler bob jones nathan moore 

the program takes these names 1 @ time , turns them like:

kyle.butler@emailaddress.com 

this address stored line line in new text file called final.txt

problem is, can't work, gives me segmentation fault , not writing final.txt

#include <stdio.h> #include <stdlib.h> #include <string.h>  void write(char line[100]);  int main() {     file *fp;     fp = fopen("original.txt", "r+");      char line[100];     char mod[30]="@fakeemail.com\n";     while (fgets(line, 100, fp) != null){         int i;         for(i=0; i<100; ++i){             if(line[i]==' '){                 line[i]='.';             }             if(line[i]=='\n'){                 line[i]='\0';             }             strcat(line, mod);         }            file *fp2;         fp2 = fopen("final.txt", "a");          if (fp2 != null){             fputs(line, fp2);             fclose(fp2);         }      }      fclose(fp);          return 0; } 

there several problems code, segmentation fault caused for loop:

for(i=0; i<100; ++i){     if(line[i]==' '){         line[i]='.';     }     if(line[i]=='\n'){         line[i]='\0';     }     strcat(line, mod); } 

every time through loop concatenating mod line. since iterate loop 100 times no other option quit loop, , line 100 characters long, write past 100th character of line other part of memory.