foo.c: In function 'main':
foo.c:6:9: warning: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
    6 |         scanf("%d %d",&a,&b);
      |         ^~~~~
foo.c:1:1: note: include '<stdio.h>' or provide a declaration of 'scanf'
  +++ |+#include <stdio.h>
    1 | 
foo.c:6:9: warning: incompatible implicit declaration of built-in function 'scanf' [-Wbuiltin-declaration-mismatch]
    6 |         scanf("%d %d",&a,&b);
      |         ^~~~~
foo.c:6:9: note: include '<stdio.h>' or provide a declaration of 'scanf'
foo.c:7:9: warning: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
    7 |         printf("%d",a+b);
      |         ^~~~~~
foo.c:7:9: note: include '<stdio.h>' or provide a declaration of 'printf'
foo.c:7:9: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
foo.c:7:9: note: include '<stdio.h>' or provide a declaration of 'printf'

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