/in/foo.c: In function 'main':
/in/foo.c:22:9: warning: format '%s' expects argument of type 'char *', but argument 2 has type 'char (*)[15]' [-Wformat=]
 scanf("%s",&stu[i].name);
         ^
/in/foo.c:28:9: warning: format '%s' expects argument of type 'char *', but argument 2 has type 'char (*)[15]' [-Wformat=]
 scanf("%s",&ren);
         ^
/in/foo.c:42:1: warning: implicit declaration of function 'system' [-Wimplicit-function-declaration]
 system("pause");
 ^~~~~~
/in/foo.c: In function 'cmp':
/in/foo.c:17:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^