C/C++ • invalid operands to binary

Code:

float   measure_distance(){    float   distance_cm = 0.0;    gpio_set_input_enabled( ECHO_PIN, 1 );    gpio_put( TRIGGER_PIN, 0 ); // 设置低电平    sleep_ms(2);                // 等待    uint echo_pin = gpio_get( ECHO_PIN);// printf("\nPulsed the pin high echo pin is %d", echo_pin );    gpio_put( TRIGGER_PIN, 1);  // 设置高电平    sleep_ms( 10 );             // 等待三毫秒    gpio_put( TRIGGER_PIN, 0);  // 开关触发低电平，再次让SR04发送脉冲    /*The echo pin outputs a pulse between 150 micro-seconds and 25 mili-seconds, or if no object is found, it will send a 38 ms pulse. speed of sound is 343 meters per second. This would depend upon the elevation and hummidity, but sufficiently accurate for our application.         回声引脚输出的脉冲在150微秒到25毫秒之间，或者如果没有找到物体，它将发送38毫秒的脉冲。        声速是每秒343米。这将取决于海拔和湿度，但对我们的应用来说足够准确。speed = distance travelled / time taken        速度 = 距离 / 时间so, distance = (speed * time taken)/2 -- Divide by 2 because we are listening to the echo        所以，距离 = (速度 * 时间)/2 -- 需要除以2，因为我们需要顾及 回声[echo]Now, speed of sound is 343 meters/second, whch is 3.43 centimeters per second, which is        现在，声速是343米/秒，也就是3.43厘米每秒，也就是3.43/ 1000000 = 0.0343 cm/microsecond. 3.43/ 1000000 = 0.0343 厘米 / 微秒. */    absolute_time_t  listen_start_time = get_absolute_time();    absolute_time_t  max_wait_time  = delayed_by_ms( listen_start_time, 30 );      // No point waiting more than 30 Mili sec. // 没必要等待超过30毫秒    do{        absolute_time_t  t_now = get_absolute_time();        //int64_t  t_now = get_absolute_time();        // 获取绝对时间戳        if(t_now > max_wait_time) {            break;        }        echo_pin = gpio_get( ECHO_PIN);        if( echo_pin != 0 ){   // 我们收到了回声            absolute_time_t  first_echo_time = t_now;            printf(" the pin went high ");            while(echo_pin == 1 && t_now < max_wait_time){                echo_pin = gpio_get( ECHO_PIN );                t_now = get_absolute_time();            }printf(" pin is at %d", echo_pin );if( echo_pin == 1 ){break;// 返回值 0cm}//printf("Start %llu ", listen_start_time );//printf( " end %llu ", t_now );            int64_t pulse_high_time = absolute_time_diff_us( first_echo_time, t_now );float pulse_high_time_float = (float) pulse_high_time;            printf(" High Time %f ", pulse_high_time_float );             distance_cm = pulse_high_time_float * 0.01715; //pulse_high_time_float / 58.0 ;            break;        }    }    while( true );    gpio_set_input_enabled( ECHO_PIN, 0 );    return distance_cm;}