cast variable to int vs round() function

Question

I have seen it in several places where (int)someValue has been inaccurate and instead the problem called for the round() function. What is the diff

Answer 1

1. Casting to int truncates a floating-point number, that is, it drops the fractional part.
2. The round function returns the nearest integer. Halfway cases are rounded away from zero, for example, round(-1.5) is -2 and round(1.5) is 2.

7.12.9.6 The round functions

Synopsis

#include 
double round(double x);
float roundf(float x);
long double roundl(long double x);

Description

The round functions round their argument to the nearest integer value in floating-point format, rounding halfway cases away from zero, regardless of the current rounding direction.

Returns

The round functions return the rounded integer value.

Source: the C99 standard (ISO/IEC 9899:1999). This section did not change in the C11 standard (ISO/IEC 9899:2011).

(For those who are interested, here is a clear introduction to rounding algorithms.)