C: How to increment after entering an if statement - c

Question

I am trying to enter an if statement when my counter reaches the value 51, and then increment the counter inside the if statement so that it is never true again:
void imu_raw_handler (const lcm_recv_buf_t *rbuf, const char *channel,
const imu_raw_t *msg, void *userdata) {
for(counter = 1; counter < 51; counter++)
{
gyro_roll = (gyro_roll + gyro_roll_old*(counter-1))/counter;
gyro_pitch = (gyro_pitch + gyro_pitch_old*(counter-1))/counter;
gyro_yaw = (gyro_yaw + gyro_yaw_old*(counter-1))/counter;
accel_x = (accel_x + accel_x_old*(counter-1))/counter;
accel_y = (accel_y + accel_y_old*(counter-1))/counter;
accel_z = (accel_z + accel_z_old*(counter-1))/counter;
}
if (counter == 51){
// set zero points
axo = accel_x;
ayo = accel_y;
azo = accel_z;
gro = gyro_roll;
gpo = gyro_pitch;
gyo = gyro_yaw;
printf("Ready for Takeoff\n");
counter++;
}
}
Edit: My main function looks like this. It is supposed to subscribe to a streaming topic for as long as it is running. I define a counter as a global variable.
int main()
{
lcm_t *lcm = lcm_create(NULL);
imu_raw_t_subscribe(lcm, "IMU_RAW", imu_raw_handler, NULL);
// Enter read loop
while (1) {
if(!lcm_handle_timeout(lcm, 1000)) {
printf("Failed read from IMU_RAW channel\n");
}
}
lcm_destroy(lcm);
}
But this will repeatedly print my message forever rather than making counter = 52 and never happening again. Why does this not work?

Answer 1

The problem most likely exists outside these code snippets. Please check if you have no prints somewhere else.

Answer 2

The problem is because you call that function in a while, and because of
for(counter = 1; counter < 51; counter++)
the counter will become again 51 (everytime the function is called) and then will enter again in that if (counter == 51).
To resolve that you could declare a global variable int ok = 0; and use it like this:
void imu_raw_handler (const lcm_recv_buf_t *rbuf, const char *channel,
const imu_raw_t *msg, void *userdata) {
for(counter = 1; counter < 51; counter++)
{
gyro_roll = (gyro_roll + gyro_roll_old*(counter-1))/counter;
gyro_pitch = (gyro_pitch + gyro_pitch_old*(counter-1))/counter;
gyro_yaw = (gyro_yaw + gyro_yaw_old*(counter-1))/counter;
accel_x = (accel_x + accel_x_old*(counter-1))/counter;
accel_y = (accel_y + accel_y_old*(counter-1))/counter;
accel_z = (accel_z + accel_z_old*(counter-1))/counter;
}
if (ok == 0){ //will enter here once, only if you don't modify the ok anytime
// set zero points
axo = accel_x;
ayo = accel_y;
azo = accel_z;
gro = gyro_roll;
gpo = gyro_pitch;
gyo = gyro_yaw;
printf("Ready for Takeoff\n");
ok = 1; //this will be done once
}
}
I hope this is correct.

Answer 3

The for loop right before the if uses the counter variable, so every time the loop is finished, counter will be 51.
My guess is that the loop shouldn't be there at all, it doesn't seem to make any sense.