A millisecond Timer in C

Here is one possible implementation of a millisecond timer in C using time.h and ts.tv_nsec
Proof of concept:  Timer Source code

A simpler, more compliant version can be found in repository.
#include <stdio.h> #include <stdlib.h> #include <time.h> typedef struct nTimer{ int ms; //milliseconds long oldtime; //to calculate increment in time long oldticks; //to calculate increment in no. of ticks long ticks; //how many ticks have been made long elapsed; //total time elapsed in ms } NTIMER; /* Miliseconds timer */ int timer1(NTIMER *mytimer1){ struct timespec ts; long get_ms; long res, res2; if (mytimer1->ticks == 0){ //First tick, set up values mytimer1->oldtime = 0; mytimer1->ticks = 1; mytimer1->oldticks = 1; mytimer1->elapsed = 0; return 1; } else{ //subsequent ticks timespec_get(&ts, TIME_UTC); //Getms gets 10^-3 milleseconds get_ms = (ts.tv_nsec % 10000000) / 1000000; //Add a millisecond every time a change is detected in 10^-3 res = get_ms-mytimer1->oldtime; if(abs(res) >= 1){ mytimer1->elapsed = mytimer1->elapsed + 1; mytimer1->oldtime = get_ms; } //Calculate tick by divided time elapsed with ms requested res2 = mytimer1->elapsed / mytimer1->ms; if (res2 == mytimer1->oldticks) { mytimer1->ticks = mytimer1->ticks + 1; mytimer1->oldticks = mytimer1->oldticks+1; return 1; } else return 0; } } int main(){ NTIMER mytimer1; int i=0; char msg[13] = "Hello there!\0"; /* INIT TIMER */ //mytimer1.ticks must be set to 0 at start. mytimer1.ms = 30; mytimer1.ticks = 0; do{ if (timer1(&mytimer1) == 1) { printf("%c\n", msg[i]); i++; } } while (mytimer1.ticks < 13); printf("Total elapsed time in ms: %ld", mytimer1.elapsed); }

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A one-line formula to add the digits of a 2-digit number using mod

Adding two digits of a number is the same as subtracting 9 multiplied by the number in the tens from the original number. This formula uses mod(%) to isolate such number and provides the result of the addition of the 2 digits of a given number from 11 to 99:

From: x- (((x -(x mod 10)) / 10) *9)
To: f(x) = x - (1/10(x - x mod 10))× 9

Example: 23 -> 2+3 = 5 | 23 - (9*2) = 5 | 23 - (((23 - (23 mod 10)) / 10) * 9) = 5 

Sample in C: twodigits

Asteroid Game

Screenshot of the remake of the classic game Asteroid with SDL2 in pure C.

[+] Code:

First commit and subsequent development: 

https://github.com/velorek1/asteroid

[+] Game Structure: