Initialization of global and static variables in C

Predict the output of following C programs.

// PROGRAM 1 
#include <stdio.h> 
#include <stdlib.h> 
  
int main(void) 
{ 
   static int *p = (int*)malloc(sizeof(p)); 
   *p = 10; 
   printf("%d", *p); 
} 

// PROGRAM 2 
#include <stdio.h> 
#include <stdlib.h> 
int *p = (int*)malloc(sizeof(p)); 
  
int main(void) 
{ 
    *p = 10; 
    printf("%d", *p); 
} 

Both of the above programs don’t compile in C. We get the following compiler error in C.

error: initializer element is not constant

In C, static and global variables are initialized by the compiler itself. Therefore, they must be initialized with a constant value.

Note that the above programs compile and run fine in C++, and produce the output as 10.

As an exercise, predict the output of following program in both C and C++.

#include <stdio.h> 
int fun(int x) 
{ 
    return (x+5); 
} 
  
int y = fun(20); 
  
int main() 
{ 
    printf("%d ", y); 
}

This article is contributed by Shankar Shastri. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.

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