MLGetType()

#include "mathlink.h"

/* read the type of the expression from a link */

void f(MLINK lp)
{
    switch(MLGetType(lp))
    {
        case MLTKINT:
            /* read the integer */
        case MLTKREAL:
            /* read the floating point number */
        case MLTKSTR:
            /* read the string. */

        /* ... */
    }
}