Redeclaration of global variable in C

Consider the below two programs:

// Program 1
int main()
{
   int x;
   int x = 5;
   printf("%d", x);
   return 0;
}

Output in C:

redeclaration of ‘x’ with no linkage

// Program 2
int x;
int x = 5;

int main()
{
   printf("%d", x);
   return 0;
}

Output in C:

5

In C, the first program fails in compilation, but second program works fine. In C++, both programs fail in compilation.

C allows a global variable to be declared again when first declaration doesn’t initialize the variable.

The below program fails in both C also as the global variable is initialized in first declaration itself.

int x = 5;
int x = 10;

int main()
{
   printf("%d", x);
   return 0;
}

Output:

 error: redefinition of ‘x’

This article is contributed Abhay Rathi.