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Yoshi
Yoshi

Reputation: 55

Convert from milliseconds to microseconds and store in double in C

Hi I'm trying to convert DELAY from milliSeconds into microSeconds and store it in a double. But when I use the below code it produces the output 0.000000 On a calculator it works as the desired outcome I'm after if 500 is the DELAY is 0.500000 so I can use it with 'struct timeval'.

#define DELAY 500
double num = (DELAY / 1000);

printf("Num: %lf",num);

Upvotes: 1

Views: 2750

Answers (3)

Shafik Yaghmour
Shafik Yaghmour

Reputation: 158629

This will use integer division:

 double num = (DELAY / 1000);

If you change the 1000 to a floating constant then you will obtain the result you want:

double num = (DELAY / 1000.0);

this works because division will perform the usual arithmetic conversions on it's operands which in this case will cause DELAY to be converted to a double as well.

Note It is probably worth noting that if you want to convert from milliSeconds into microSeconds you want to multiply by 1000 not divide.

Upvotes: 2

Ed Heal
Ed Heal

Reputation: 60037

It does the division as integers and then converts

Try:

#define DELAY 500f
double num = (DELAY / 1000f);

printf("Num: %lf",num);

Upvotes: 0

Crowman
Crowman

Reputation: 25946

This:

(DELAY / 1000);

is integer arithmetic, and evaluates to zero when DELAY is less than 1000, change to:

(DELAY / 1000.0);

Upvotes: 3

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