Comparing strings with if else - c

Question

I want to make a program that has a key to open. But when i comparing the key and the input, it always says "Wrong":
#include <stdio.h>
int main(){
char key[5]="april",ckey[5];
printf("Enter the key: ");
scanf("%s",ckey);
if(ckey==key){
printf("Correct.");
}
else{
printf("Wrong.");
}
return 0;
}
Is it possible to solve the problem without using other libraries?

Answer 1

You have to leave space before "%s" inside the scanf statement,so that the '\n character is not stored in ckey to ensure success of comparison.note: ckey must have size 6 or more.
#include <stdio.h>
#include <string.h>
int main(){
char key[] = "april",ckey[6];
printf("Enter the key: ");
scanf(" %5s",ckey);
if(!strcmp(ckey, key)){
printf("Correct.");
}
else{
printf("Wrong.");
}
return 0;
}

Answer 2

you have to check character by character.
try this code :
int main(){
int i = 0 ; int j = 1;
char key[6]="april",ckey[6];
printf("Enter the key: ");
scanf("%s",ckey);
for(i = 0; i < 6; i++){
if(ckey[i] != key[i])
j=0;
}
if(j == 1)
printf(%s,"Correct.");
else
printf(%s,"Wrong.");
return 0;
}

Answer 3

You make several mistakes in array sizing for your keys. Remember, a C string is always terminated by a nul character and you must account for this when you size your arrays to accept such strings.
scanf is unsafe, don't use it. Use fgets instead. A safe use of fgets is:
fgets (buffer, sizeof(buffer), stdin);
The answer to your question is no, it would be better to use strcmp if you want to lexically compare strings in C and that would involve including the header. But even so, this is not adding any other "libraries" since fgets and strcmp are in the same standard C library.
If you must not add any other headers (which makes no sense if this is part of a larger project but makes perfect sense if this is a homework problem) then you can write your own strcmp (we'll call it compare here) and call it from main.
#include <stdio.h>
int compare (const char* src, const char* dst)
{
int ret = 0;
while( ! (ret = *src - *dst) && *dst){
++src, ++dst;
}
if ( ret < 0 )
ret = -1 ;
else if ( ret > 0 )
ret = 1 ;
return( ret );
}
int main(void){
char key[6]="april",ckey[6];
printf("Enter the key: ");
fgets(ckey, sizeof ckey, stdin);
if(!compare(key,ckey)) {
printf("Correct.");
}
else {
printf("Wrong.");
}
return 0;
}
A better use of your time would be to write it using the functions available to you in the standard C library:
#include <stdio.h>
#include <string.h>
int main(void){
char key[6]="april",ckey[6];
printf("Enter the key: ");
fgets(ckey, sizeof ckey, stdin);
if(!strcmp(key,ckey)) {
printf("Correct.");
}
else {
printf("Wrong.");
}
return 0;
}
But even this solution has a flaw. It will accept "aprilaaaa" or any string beginning with "april" as a valid ckey. Can you explain why? How would you fix this?

Answer 4

In the condition of the if statement
if(ckey==key){
there are compared two addresses of the memory areas occupied by the arrays.
So you will always get false because the arrays occupy different memory areas.
If you may not use other standard functions as for example strncmp or memcmp declared in header <string.h> then you can write the following way
#include <stdio.h>
int main( void ){
char key[5]="april",ckey[6];
printf("Enter the key: ");
scanf("%5s",ckey);
size_t i = 0;
while ( i < sizeof( key ) && key[i] == ckey[i] ) ++i;
if( i == sizeof( key ) ){
printf("Correct.");
}
else{
printf("Wrong.");
}
return 0;
}
Instead of scanf it would be better to use fgets. In this case the size of the array ckey must be increased.
This declaration
char key[5]="april";
is totally valid in C though is not valid in C++.:)