MLPutString()

#include "mathlink.h"

/* send a string representing an expression to a Mathematica kernel
   for evaluation */

void f(MLINK lp)
{
    /* construct the packet to be sent to the kernel */
    MLPutFunction(lp, "EvaluatePacket", 1);
    MLPutFunction(lp, "ToExpression", 1));
    MLPutString(lp, (const char *)"3+4/Sqrt[19.2]", 14));
    MLEndPacket(lp));

    /* send the packet */
    if(! MLFlush(lp))
        { /* unable to flush an outgoing data buffered in lp */ }

}