foo.c:1:1: warning: return type defaults to 'int' [-Wimplicit-int]
    1 | main(){
      | ^~~~
foo.c: In function 'main':
foo.c:4:19: warning: implicit declaration of function 'putchar' [-Wimplicit-function-declaration]
    4 | for (j=1;j<=5;j++)putchar('*');
      |                   ^~~~~~~
foo.c:1:1: note: include '<stdio.h>' or provide a declaration of 'putchar'
  +++ |+#include <stdio.h>
    1 | main(){
foo.c:5:1: warning: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
    5 | printf("\n");
      | ^~~~~~
foo.c:5:1: note: include '<stdio.h>' or provide a declaration of 'printf'
foo.c:5:1: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
foo.c:5:1: note: include '<stdio.h>' or provide a declaration of 'printf'

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