/in/foo.c: In function 'main':
/in/foo.c:6:1: warning: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
 scanf("%d",&n);
 ^~~~~
/in/foo.c:6:1: warning: incompatible implicit declaration of built-in function 'scanf'
/in/foo.c:6:1: note: include '<stdio.h>' or provide a declaration of 'scanf'
/in/foo.c:23:1: warning: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
 printf("%d",k);
 ^~~~~~
/in/foo.c:23:1: warning: incompatible implicit declaration of built-in function 'printf'
/in/foo.c:23:1: note: include '<stdio.h>' or provide a declaration of 'printf'
/in/foo.c:4:17: warning: unused variable 't' [-Wunused-variable]
 int a,b,n,k=0,i,t=0;
                 ^