foo.c: In function 'mult':
foo.c:47:6: warning: unused variable 'jw' [-Wunused-variable]
 {int jw=0;
      ^~
foo.c: In function 'main':
foo.c:11:1: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
 scanf("%d%d%d%d",&x1,&n1,&x2,&n2);
 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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