foo.c:3:1: warning: return type defaults to 'int' [-Wimplicit-int]
 main()
 ^~~~
foo.c: In function 'main':
foo.c:6:1: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
 scanf("%d%d%d",&a,&b,&c);
 ^~~~~~~~~~~~~~~~~~~~~~~~
foo.c:15:1: warning: ignoring return value of 'system', declared with attribute warn_unused_result [-Wunused-result]
 system("pause");
 ^~~~~~~~~~~~~~~