Cannot re-initialize after first initialize value to integer array

Question

I first initialize 0 to counter[10], and it is OK. However, somewhere I want to re-initialize with 0 again but fail.

The error message is

[Warning] extended initializer lists only available with -std=c++11 or -std=gnu++11

#include <stdio.h>
#include <stdbool.h>

int main(void) {

  int digit, counter[10] = {0}; //Declare variable "digit" to store individual number to be compared and declare an array for the input numbers
  bool rep_digits; //Declare a boolean variable to determine whether the input numbers has repetitive numbers or none
  int n; //Declare variable "n" to store the input numbers

  while (true) { //This while loop serves as a loop for the user input
    
    printf("\nEnter a number (capped at  on this compiler): ");
    scanf("%d", &n);
    if (n == 0) { //The user input loop terminates when the user input a 0
    break;
    }
    
    printf("Repeated digits(s): \n");

    while (n > 0) { //If the condition is true, execute the arguments inside
        digit = n % 10; //Obtain the remainder of the input number
        counter[digit]++; //Increase the counter for the obtained remainder in the array
        if (counter[digit] == 2) { //If the counter of that particular remainder is equal (and only equal) to 2, print out the number
            printf("%2d\n", digit); 
            rep_digits = true;  //Set the boolean variable to true if there is a repetitive number in the input
        }
        n /= 10; //Divide the input number by 10 to determine the next number either repetitive or not
    }
        
    counter[10] = {0}; // re-initialize to 0
        
    if (rep_digits == false) { //If the boolean variable stays false then display this message
        printf("No repeated digits\n");
    } 
  }

  return 0;
}

You can't do that. If you want to set all the values to 0 you could use a loop, or you could use memset to set all the bytes to 0. You could also move the declaration with the initialization inside the while loop — Retired Ninja
– Retired Ninja, Commented Nov 11, 2020 at 5:07

csavvy · Accepted Answer · 2020-11-11 05:28:43Z

2

counter[10] = {0}; writing beyond the array size causes undefined behavior.

suppose you have array size as int counter[10], you should write only from counter[0] till counter[9]

if you want to initialize all the array elements to 0, then you can do it two ways.

int counter[10] = {0}; \\this works only at the same place where you declare
memset(counter,0,sizeof(counter)); \\ this can be done at any other place in the program

In your program replace counter[10] = {0}; with memset(counter,0,sizeof(counter));

it should work just fine.

edited Nov 11, 2020 at 5:28

answered Nov 11, 2020 at 5:05

csavvy

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5 Comments

csavvy Over a year ago

@RetiredNinja, thanks dint have a proper look at the program before, updated the answer properly by giving explanation

Brandon J Over a year ago

Thank you for the response! I was looking for an alternative way to re-initialize my array elements to 0 without it going through declaration again. You also pointed out my dumb mistake that after declaration, the array "counter[10] = {0}" where 10 is actually the index not the size of the array anymore.

csavvy Over a year ago

@BrandonJ, up voting is the only way of saying thank you here :)

Brandon J Over a year ago

I tried to vote ur answer and verify it, but I am still new to stackoverflow, it says I need more reputation

csavvy Over a year ago

I think below the down vote option there is an option to accept as answer you can click on that

Ishaan Kanwar · Accepted Answer · 2020-11-11 05:48:39Z

2

Instead of using int counter[10] = {0}

Use memset int counter[10]; memset(counter,0,sizeof(counter));

The above memset line fills every value of counter array to 0.

edited Nov 11, 2020 at 5:48

answered Nov 11, 2020 at 5:18

Ishaan Kanwar

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1 Comment

Retired Ninja Over a year ago

Worth noting that memset works on bytes, not ints, so replace that 0 with a 1 and the result will not be an array of values set to 1.

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