Why am I not getting the output when I use Strcmp? - c

Question

when I use strcmp:
#include <stdio.h>
#include <string.h>
int main(void)
{
char *i, *j;
scanf("%s %s", &i, &j);
if (strcmp(i, j) == 0){
printf("Same \n");
} else {
printf("different\n");
}
}
output: gives no output just blank
When I directly compare i & j
#include <stdio.h>
#include <string.h>
int main(void)
{
char *i, *j;
scanf("%s %s", &i, &j);
if (i == j) {
printf("Same \n");
} else {
printf("different\n");
}
}
output : Same
Ye that's all I tried by replacing i == j with strcmp().

Answer 1

The problem is not related to the use of strcmp, you have undefined behavior in the way you use scanf() to read strings. You pass the addresses of string pointers where scanf() expects addresses of char arrays.
In both cases, the behavior is undefined and indeed the first program causes a segmentation fault, whereas the second seems to produce expected behavior, only by chance because the entered strings are short. Try longer strings and you might get a segmentation fault as well.
Here is a modified version with defined behavior:
#include <stdio.h>
#include <string.h>
int main(void) {
char i[100], j[100];
if (scanf("%99s %99s", i, j) == 2) {
if (strcmp(i, j) == 0) {
printf("Same\n");
} else {
printf("Different\n");
}
}
return 0;
}
Note how %99s tells scanf() to store at most 99 bytes into the destination arrays to avoid buffer overflows.
Also note how scanf return value must be tested to avoid accessing uninitialized data (it returns the number of successful conversions, which must be 2 for both i and j to contain valid C strings).

Answer 2

I replaced the *i and *j with i[50] and j[50] respectively.
And here I avoided using &i as in case of a string (character array), the variable itself points to the first element of the array in question. Thus, there is no need to use the ‘&’ operator to pass the address.
And now this would work with strcmp
#include<stdio.h>
#include<string.h>
int main(void){
char i[50], j[50];
printf("Enter strings: ");
scanf("%s %s", i, j);
if (strcmp(i, j) == 0) printf("Same \n");
else printf("different\n");
}
input:
Enter strings: hello(enter)
hello
output: same