Question

how to solve this error (C programming)

[Warning] converting to "int" from "float"

Answer 1

if you have something that's a floating point, or another primitive, you need to convert before using it with another primitive, I.E., Casting... In Java you do

float f = 10;

int i = (Int) f;

or if you have a string.

String s + "hi";

int a = Integer.parseInt(s);

Answer 2

To be clear it is a warning and not an error, this means that your code will compile. The warning is telling you that you will lose some precision from the conversion. And as @KonradZuse pointed out, just like in Java, you use casting in C.
float f = 10.0;
int a;
a = (int)f;

Answer 3

depending on the situation it can be an error. Some things can only take in floats, or ints, and doing something else wont work at all.