Also, the strlen call needs to be moved inside the loop :
for (i=0; i<5; i++)
{
scanf( "%s", text );
printf("%s", text);
size = strlen(text)+1;
espeak_Synth( text, size, position, position_type, end_position, flags,
unique_identifier, user_data );
espeak_Synchronize();
fflush(stdout);
}