Memory Problems: buffer overflow

 enter 6 characters ("mypass")
 enter any 6 characters
 enter any 9 characters 
 enter any 10 characters

 [run on jupiter]
 a at ffbefa2f and
 x at ffbefa38
 Enter a pass word: mypass
 x = 1
 Password is correct!
================================

#include <stdio.h>
  
/*checkpasstest.c*/
int checkpass(void); // prototype

int main(void) {
   int x;
   x = checkpass(); // call function 
   
   fprintf(stderr, "x = %d\n", x); // print the value of x
   
   if (x) // if x is not zero then
      fprintf(stderr, "Password is correct!\n");
   else  // x has been returned as a zero
      fprintf(stderr, "Password is not correct!\n");
   return 0;
}

/*checkpass.c*/
#include <stdio.h>
#include <string.h>

int checkpass(void){
   int x;
   char a[9]; // an array with 9 bytes allocated
   
   x = 0; // return value if x is not changed
   fprintf(stderr,"a at %p and\nx at %p\n", (void *)a, (void *)&x);
   printf("Enter a pass word: ");
   scanf("%s", a); // read a string from user
   if (strcmp(a, "mypass") == 0) // if a is equal to "mypass"
      x = 1;
   return x;
}

$ cc -o checkpasstest checkpasstest.c checkpass.c

TRY IT!