CODEWITHSUNDEEP
cboolean
explorer
explorer

Reputation: 127

What is the default value of an uninitialized boolean array, in C?

I have something like,

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

int main()
{
    int t,answer;
    bool count;
    long long int L;
    scanf("%d",&t);
    while(t>0)
    {
        answer = 0;
        scanf(" %lld",&L);
        bool count[L];
  //  .....restofthecode. NDA Constraint.

What would be the default value of all the elements of arr[x]? Is it false always? Or true? Or any random value?

Upvotes: 0

Views: 13898

Answers (2)

ouah
ouah

Reputation: 145829

There is no type named boolean in C but there is _Bool and in stdbool.h a macro bool that expands to _Bool.

#include <stdbool.h>

#define X 42
bool arr[X];

arr elements have an initial value of false (that is 0) if declared at file scope and indeterminate if declared at block scope.

At block scope, use an initializer to avoid the indeterminate value of the elements:

void foo(void)
{
     bool arr[X] = {false};  // initialize all elements to `false`
}

EDIT:

Now the question is slightly different:

long long int x;
scanf("%lld",&x);
bool arr[x];

This means arr is a variable length array. VLA can only have block scope, so like any object at block scope it means the array elements have an indeterminate value. You cannot initialize a VLA at declaration time. You can assign a value to the array elements for example with = operator or using memset function.

Upvotes: 6

Sourav Ghosh
Sourav Ghosh

Reputation: 134316

As per your code, in local scope

boolean arr[x];

itself is invalid. x is used uninitialized.

Just FYI, in global [file] scope, all the variables are initialized to 0. In local scope, they simply contain garbage, unless initialized explicitly.

EDIT:

[After the edit] All the variables in the arr array will have garbage value. It is in local scope [auto].

Upvotes: 1

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