Can I make a while-loop that uses RSI value as the condition?

When I try to run this while-loop in MQL4, it can not seem to update the rsi from within the loop. It always returns the same value of the rsi and thus stays in an eternal loop. I have tried it on an EA as well as a script.

I have also tried making rsi a globally defined variable too but still did not work.

void OnTick()
{

     double rsi = iRSI(NULL,0,14,PRICE_CLOSE,0);        // defining rsi
                 
     while( rsi < 50 )
     {
            double rsi = iRSI(NULL,0,14,PRICE_CLOSE,0); // update rsi 
            Sleep(10000);                               // slow down loop 
            Alert("this is from inside while loop rsi is "+rsi); 
     }
        
     Alert("While loop exited, condition met");         // now code goes
     Alert("opening an order now " );                   //     to place an order
}

Can I make a while-loop that uses RSI value as the condition?

Oh sure you can.

Let's move out the colliding elements.

Given the code as-is, there are several brutal misconceptions to repair:

• if a code spends some time "inside" such a loop, there will never be heard a new incoming QUOTE-message from market, so your Close[0]-value will remain "blind" to any such update from Market.
• if a second double rsi = ... declaration takes place "inside" a scope of a while-loop-constructor, the newer versions ( Builds ) of the MQL4 language will actually "mask" the older ( "outer" ) variable, that is yet still used in the loop-constructor control variables / conditions. Result? You assign "new" values to an "inner"-variable, that bears just by coincidence a same name as the "outer"-variable ( both are named rsi, yet the "inner" keeps-masking the "outer", so the "outer" never gets any update(s), if any such were stored inside the loop into the "inner" )

Solution

• avoid masking by not declaring any same-name named variables (always, it is a sign of good engineering practice)
• avoid receiving market-QUOTE-updates by deaf-loop-locking - prefer the non-blocking use of if(){...} instead of while(){...}

MQL4 is a responsive-ecosystem, where OnTick() is automatically called whenever a new QUOTE-message arrives from FX-Market, so design your algorithms so as these never block.

For your learning-directed inspiration, you may try your next few steps using this template :

string MASK  = "[%s]_INF:: "                           // DEF. & INIT...
             + "This is a QUOTE# %5d "
             + "Having arrived at [%s]_FX-MarketTIME\n"
             + "|Ask %16.8f\n"
             + "|Bid %16.8f\n"
             + "|Vol %16d\n"
             + "|RSI %16.8f";
double rsi   = EMPTY;                                  // DEF. & INIT...
int   nTicks = 0;                                      // DEF. & INIT...

void OnDeinit( const int aDeinitReason )
{    EventKillTimer();
}

int  OnInit()
{    EventSetTimer( 1 );
     Comment( "------------------------------------------------------\n ",
                    "WAITING for a first QUOTE-arrival from FX-Market\n",
              "------------------------------------------------------"
               );
     return( 0 );
}

void OnTick()
{     nTicks++;                                        // update COUNTER
     rsi = iRSI( NULL, 0, 14, PRICE_CLOSE, 0 );        // update rsi
     Comment( SetupComment() );                        // update GUI

  // -------------------------------- FIRST 50 FX-Market Ticks delivered
     if ( nTicks < 50 ) return;

  // -------------------------------- AFTER 50 FX-Market Ticks delivered
  // --------------------------------       BE WARNED, THIS IS AN AWFUL ANTI-PATTERN
     while( True )
     {
            rsi = iRSI( NULL, 0, 14, PRICE_CLOSE, 0 ); // update rsi
            Comment( SetupComment() );                 // update GUI
            Sleep( 10000 );
     }
  // --------------------------------       NEVER GETS HERE
     Alert( "?" );
}

string SetupComment()
{      return( StringFormat( MASK,
                             TimeToStr( TimeLocal(),
                                        TIME_DATE|TIME_MINUTES|TIME_SECONDS
                                        ),
                             nTicks,
                             TimeToStr( TimeCurrent(),
                                        TIME_DATE|TIME_MINUTES|TIME_SECONDS
                                        ),
                             NormalizeDouble( Ask, 8 ),
                             NormalizeDouble( Bid, 8 ),
                             Volume[0],
                             NormalizeDouble( rsi, 8 )
                             )
               );
}

void OnTimer()
{    Comment( ChartGetString( 0, CHART_COMMENT ),
              "\n",
              TimeToStr( TimeLocal(),
                         TIME_DATE|TIME_MINUTES|TIME_SECONDS
                         )
              );
     Print(   ChartGetString( 0, CHART_COMMENT ) );
}