为什么这个整数除法产生0？

Question

Could someone tell me why the following code is outputting 0 at the marked line?

It seems as if everything is correct but then when I try to get the result near the end it's giving me 0 each time.

#include <stdio.h>

int main() {

    // Gather time-lapse variables

    int frameRate, totalLengthSecs;
    printf("How many frames per second: ");
    scanf("%i", &frameRate);
    printf("--> %i frames confirmed.", frameRate);
    printf("\nDesired length of time-lapse [secs]: ");
    scanf("%i", &totalLengthSecs);
    printf("--> %i seconds confirmed.", totalLengthSecs);
    int totalFrames = frameRate * totalLengthSecs;
    printf("\nYou need %i frames.", totalFrames);

    // Time-lapse interval calculation

    int timeLapseInterval = totalLengthSecs / totalFrames;

    printf("\n\n%i", timeLapseInterval); // <-- this prints 0

    return 0;
}

Answer 1

In short: Integer division truncates

You need the following:

double timeLapseInterval = (double) totalLengthSecs / (double)totalFrames;
printf("\ntimeLapseInterval : %f \n", timeLapseInterval);

Answer 2

You are performing integer math.

Math between two integers will produce an integer. And the result will be rounded towards zero.

This line:

totalLengthSecs / totalFrames;

Is likely producing a result that's between 0 and 1 . And getting rounded to 0

Answer 3

You are printing integers and therefore it will round down the value.

timeLapseInterval / totalFrames will be (1 / frameRate) which will be < 1 unless frameRate is 1 (or 0 in which case you have an error dividing by 0)

Answer 4

When you divide 2 numbers in C and the denominator is integer, the compiler intends it as an integer division. Therefore, if you divide 1 divided 2, it returns zero and not 0.5

Moreover, your output variable is an integer too, hence, if you expect decimal outputs, you won't get it.

You can fix it by doing:

float timeLapseInterval = totalLengthSecs / (float)totalFrames;

printf("\\n\\n%f", timeLapseInterval);

I hope this helps