compare 2 inputs from keyboard with strcmp leads to segmentation fault

Question

I am new student in c language and I just come up with this. I code:

#include <stdio.h>
#include <string.h>

int main(void)
{
   char str[80];

   printf("Enter sth: ");
   char st1 = gets(str);

   printf("Enter sth: ");
   char st2 = gets(str);

   if(strcpy(st1,st2))
     printf("Same\n");
   else
      printf("Different\n");

  return 0;
}

My goal is to check if the 2 strings i enter from the keyboard are the same. I compile it and i get some warnings:

hello.c: In function ‘main’: hello.c:9:16: warning: initialization makes integer from pointer without a cast [enabled by default]

hello.c:12:16: warning: initialization makes integer from pointer without a cast [enabled by default]

hello.c:14:5: warning: passing argument 1 of ‘strcpy’ makes pointer from integer without a cast [enabled by default]

/usr/include/string.h:128:14: note: expected ‘char * restrict’ but argument is of type ‘char’

hello.c:14:5: warning: passing argument 2 of ‘strcpy’ makes pointer from integer without a cast [enabled by default]

/usr/include/string.h:128:14: note: expected ‘const char * restrict’ but argument is of type ‘char’

Enter sth: asd
Enter sth: asd
Output: Segmentation fault (core dumped)

Segmentation Fault i saw that is an error when you want to access sth that it doesnt exist!

I search it a little here in Stackoverflow with similar questions and here but i dont understand why this code isnt working. Thank you!

Answer 1

You are treating an address of char variable as string and using strcpy instead of strcmp. This:

char st1 = gets(str);
char st2 = gets(str);
if(strcpy(st1,st2))

was meant to be:

char st1[255], st2[255];
scanf("%254s", st1);
scanf("%254s", st2);
if(strcmp(st1, st2) == 0)

Answer 2

 if(strcpy(st1,st2))
      ^
      |
    strcmp

strcpy is for string copy, not for string compare.
To remove segmentation fault change char str1 to char *str and char str2 to char *str2.

#include <stdio.h>
#include <string.h>

int main(void)
{
    char str1[80];
    char str2[80];

    printf("Enter sth: ");
    char *st1 = gets(str1);

    printf("Enter sth: ");
    char *st2 = gets(str2);

    if(!strcmp(st1,st2))
        printf("Same\n");
    else
        printf("Different\n");

    return 0;
} 

Answer 3

You get the compile warnings because gets() returns char *, but you declare str1 and str2 as char.

You get the segmentation fault because it should be:

if(strcpy(st1,st2))

should be used with strcmp, I guess it's a typo because strcmp is in your question's tag :)

Note: Never use gets(), you can use fgets() instead.

char *st1 = fgets(str, 80, stdin);

Answer 4

you are trying to use strcmp but you using strcpy.

This code may help you.

#include <stdio.h>
#include <string.h>

int main(void)
{
   char str1[80];
   char str2[80];

   printf("Enter sth: ");
   gets(str1);

   printf("Enter sth: ");
   gets(str2);

   if(!strcmp(str1,str2))
     printf("Same\n");
   else
      printf("Different\n");

  return 0;
}

Answer 5

Here is how to fix your code :

#include <stdio.h>
#include <string.h>

int main(void)
{
   char str[80];
   char str2[80];

   printf("Enter sth: ");
   //notice that gets is not safe,
   //if the line is too long (>79 char), you'll have a buffer overflow
   gets(str);

   printf("Enter sth: ");
   gets(str2);

   //strcmp instead of strcpy
   if(strcmp(str,str2) == 0)
     printf("Same\n");
   else
      printf("Different\n");

  return 0;
}