Use an idle-loop to allow your robot to "hang out" at a particular task until a condition is met.

Idle Loop, VEX V5, rangefinder, 3-wire

// ----------------------------------------------------------------------------
//                                                                            
//    Project:        3-Wire Rangefinder Sensing                                      
//    Description:    This example will show all of the available commands
//                    for using the 3-Wire Rangefinder Sensor                       
//    Configuration:  V5 Speedbot (Drivetrain 2-motor, No Gyro)
//                    Rangefinder in 3-Wire Ports A B
//                                                                            
// ----------------------------------------------------------------------------

#include "vex.h"

using namespace vex;

// Begin project code

int main() {
    Drivetrain.setDriveVelocity(30, percent);
    wait(0.2,seconds);
    
    Drivetrain.drive(forward);

    Brain.Screen.clearScreen();
    Brain.Screen.setCursor(1,1);
    Brain.Screen.print("Found Object?: %s", RangeFinderA.foundObject() ? "TRUE" : "FALSE");
    Brain.Screen.newLine();
    Brain.Screen.print("Distance - Inches: %.2f", RangeFinderA.distance(inches));
    Brain.Screen.newLine();
    Brain.Screen.print("Distance - MM: %.2f", RangeFinderA.distance(mm));
    Brain.Screen.newLine();

    //A brief delay to allow text to be printed without distortion or tearing
    wait(50, msec);

    while (RangeFinderA.distance(mm) > 300) {
        wait(50, msec);
    }
     
        Drivetrain.stop();
        wait(0.5,seconds);
}