Error "initializer element is not constant" when allocate the memory

  1 #include<stdio.h>
  2 #include<malloc.h>
  3 
  4 typedef struct node_t{
  5     int i;
  6     struct node_t* link;
  7 }node;
  8 
  9 node* head = (node *)malloc(sizeof(node));
 10 
 11 if(head == NULL){
 12     printf("\n malloc for head node failed! \n");
 13 }
 14 
 15 int main(){
 16     int i = 10;
 17     node* temp = NULL;
 18     temp = (node *)malloc(sizeof(node));
 19     if(temp == NULL){
 20         printf("\n malloc for temp node failed! \n");
 21     }
 22     else{
 23         while(i<=10){
 24             ;
 25         }
 26     }
 27     return 0;
 28 } 

compilation error:

linked.c:9:1: error: initializer element is not constant
linked.c:11:1: error: expected identifier or ‘(’ before ‘if’

I'm trying a simple linked list programme. It's not fully completed. I'm getting a compilation error. Couldn't understand why this happened.

Since you're defining head as a global, its initializer needs to be a constant--basically, the compiler/linker should be able to allocate space for it in the executable, write the initializer into the space, and be done. There's no provision for calling malloc as you've done above during initialization--you'll need to do that inside of main (or something you call from main).

#include <stdlib.h>

void init() { 
    head = malloc(sizeof(node));
}

int main() { 
    init();
    // ...
}

In this case, the code you have in main never actually uses head though, so you may be able to skip all of the above without a problem.