printf signature is
int printf ( const char * format, ... );The first parameter is the format string and all the following parameters are the format specifiers (subsequences beginning with %).
printf("%d \n","%d",a,b);The code above invokes undefined behaviour because the first format specifier %d is used to present decimal integer value while the parameter matching this specifier is "%d" which has type const char *.
You should change it to:
printf("%d %d\n",a,b);