why do we put %d

Answer 1

C uses formatted output. The 'printf' function has a special formatting character (%) — a character following this defines a certain format for a variable:

%c — characters
%d — integers
%f — floats

e.g. printf("%c %d %f", ch, i, x);

Answer 2

Furthering to ÃKR ,
you can use scanf for taking input:
scanf("%c %d %f",&ch,&i,&x);
Note that:you have to use a & operator which indicates the address of ch,i and x variable .