float variables in C [duplicate]

Answer 1

Here's a brief analysis of your code:

int a = 9/5; // 9/5 = 1.8, but since you are doing integer division and storing the value in an integer it will store 1.
printf("%f\n", a);//Using incorrect format specifiers with respect to datatypes, will cause undefined behavior

printf("%d\n",a);//This should print 1. And correct.

Or if you want the float:

instead of int use float :

   float a=9.0f/5;//This will store 1.800000f
   //float a=9/5 will store 1.000000 not, 1.8 because of integer divison 
   printf("%f\n",a); //This will print 1.800000

Also do read this: http://en.wikipedia.org/wiki/IEEE_754-2008 on how floating points work.

Clarification about integer division:

C99: 6.5.5 Multiplicative operators

6 When integers are divided, the result of the / operator is the algebraic quotient with any fractional part discarded.⁸⁸⁾ If the quotient a/b is representable, the expression (a/b)*b + a%b shall equal a

⁸⁸⁾ This is often called ‘‘truncation toward zero’’.