(Float) Typecast in C

Question

I am currently learning C and typecasts and it is suggesting that if I want to convert an int to a float I should precede the variable with (float) to do this.

However, when I don't use the typecast, the answer still comes out correct, even though I am mixing the ints and floats.

Can someone explain why/when I would need to use the typecast (float) in particular?

#include <stdio.h>

int main(void) {
    int A, B, E;
    float C, D;

    A = 2;
    B = 1;
    C = 12.5;

    D = C * A + B;
    E = C * A + B;

    printf("Total is %.1f\n", D);
    printf("total is %d", E);
    return 0;
}

Answer 1

You never need to explicitly typecast to float unless you want to force a precise operation between to ints, for example

int a = 10;
int b = 3;

a / b yields 3 of type int (because it's an integer division), while a / (float)b yields 3.3333.. of type float.

C language specification in addition ensures you that an integer type can be implicitly converted to a float whenever it's necessary to do so (eg. an operation with another float). In addition narrowing can occur if you assign a float value to an int variable, in that case value is truncated. (§6.3.1.4 of C11)