/in/foo.c: In function 'main':
/in/foo.c:5:2: warning: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
  scanf("%d", &a);
  ^~~~~
/in/foo.c:5:2: warning: incompatible implicit declaration of built-in function 'scanf'
/in/foo.c:5:2: note: include '<stdio.h>' or provide a declaration of 'scanf'
/in/foo.c:13:2: warning: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
  printf("%d", cnt);
  ^~~~~~
/in/foo.c:13:2: warning: incompatible implicit declaration of built-in function 'printf'
/in/foo.c:13:2: note: include '<stdio.h>' or provide a declaration of 'printf'
/in/foo.c:14:2: warning: implicit declaration of function 'system' [-Wimplicit-function-declaration]
  system("pause");
  ^~~~~~
/in/foo.c:3:18: warning: unused variable 'flag' [-Wunused-variable]
  int a,b,cnt = 0,flag = 1;
                  ^~~~