Comparing the contents of arrays in C - c

Question

Does anyone know why my code is printing "Incorrect PIN entered"
after the if statement, instead of "Correct PIN entered"? When I change the if statement to (input_pin != current_pin) it works.
#include <stdio.h>
#define PIN_SIZE 4
main()
{
int input_pin[PIN_SIZE];
int current_pin[PIN_SIZE] = {1,2,3,4};
int i;
for(i = 0; i < PIN_SIZE; i++)
{
printf("Enter PIN %d: ", i+1);
scanf("%d", &input_pin[i]);
}
if(input_pin == current_pin)
{
printf("\nCorrect PIN entered.\n");
}
else
{
printf("\nIncorrect PIN entered!\n");
}
flushall();
getchar();
}

Answer 1

The if(input_pin == current_pin) is comparing two integer arrays. In C, arrays are represented internally as pointers. It's just as if you were comparing two int * variables. Because input_pin and current_pin are actually different arrays, the two pointers will never compare as equal.
To accomplish the comparison you're trying to make, you will need to compare each element of each PIN individually.

Answer 2

You do not have to use an array in this case
#include <stdio.h>
int main()
{
int input_pin = 0;
int current_pin = 1234;
printf("Enter PIN: ");
if ( ( scanf("%d", &input_pin)) == 1) { // successful scanf == 1. one item read
if(input_pin == current_pin)
{
printf("\nCorrect PIN entered.\n");
}
else
{
printf("\nIncorrect PIN entered!\n");
}
getchar();
}
}
EDIT:
Using a char array will be easier as strcmp will compare all the elements. If all the elements match, strcmp will return 0. the char arrays must be '\0' terminated.
#include<stdio.h>
#include<string.h>
#define PIN_SIZE 4
int main()
{
int i = 0;
char input_pin[PIN_SIZE+1] = {0}; // PINSIZE+1 to allow for terminating '\0'. set all elements five elements to 0
char current_pin[PIN_SIZE+1] = {"1234"};
for( i = 0; i < PIN_SIZE; i++)
{
printf("Enter PIN %d: ", i+1);
scanf(" %c", &input_pin[i]); // skip whitespace scan one character
}
if(strcmp( input_pin,current_pin) == 0) // if all elements match == 0
{
printf("\nCorrect PIN entered.\n");
}
else
{
printf("\nIncorrect PIN entered!\n");
}
getchar();
return 0;
}
An int array can be used but a flag will be needed allow for checking each element
#include<stdio.h>
#include<string.h>
#define PIN_SIZE 4
int main()
{
int i = 0;
int isMatch = 1; // flag to check matching elements
int input_pin[PIN_SIZE] = {0}; // set all elements to 0
int current_pin[PIN_SIZE] = {1,2,3,4};
for( i = 0; i < PIN_SIZE; i++)
{
printf("Enter PIN %d: ", i+1);
scanf("%d", &input_pin[i]);
if( input_pin[i] != current_pin[i]) // check each element
{
isMatch = 0; // if an element does not match, reset to 0
}
}
if( isMatch == 1) // isMatch did not get reset to 0
{
printf("\nCorrect PIN entered.\n");
}
else
{
printf("\nIncorrect PIN entered!\n");
}
getchar();
return 0;
}