I got it. Instead of using 1/3 or 1.0/3.0 you should use 0.333. You will get the right answer.
#include<stdio.h>
#include<math.h>
main()
{
float a,b;
printf("Enter the number you want to find cube root of : ");
scanf("%f",&a);
printf("The number you entered is : %.2f\n",a);
b = pow(a,0.333);
printf("The cube root of the number = %.2f",b);
}