Use enumeration constants for the voice gender field values.

src/include/espeak-ng/espeak_ng.h

 	ENOUTPUT_MODE_SPEAK_AUDIO = 0x0002,
 } espeak_ng_OUTPUT_MODE;
 
+typedef enum {
+	ENGENDER_UNKNOWN = 0,
+	ENGENDER_MALE = 1,
+	ENGENDER_FEMALE = 2,
+	ENGENDER_NEUTRAL = 3,
+} espeak_ng_VOICE_GENDER;
+
 /* eSpeak NG 1.49.0 */
 
 typedef struct espeak_ng_ERROR_CONTEXT_ *espeak_ng_ERROR_CONTEXT;

src/libespeak-ng/readclause.c

 			voice_name_specified = 1;
 			strcpy(voice_name, sp->voice_name);
 			language[0] = 0;
-			voice_select.gender = 0;
+			voice_select.gender = ENGENDER_UNKNOWN;
 			voice_select.age = 0;
 			voice_select.variant = 0;
 		}
 			if (voice_name_specified == 0)
 				voice_name[0] = 0; // forget a previous voice name if a language is specified
 		}
-		if (sp->voice_gender != 0)
+		if (sp->voice_gender != ENGENDER_UNKNOWN)
 			voice_select.gender = sp->voice_gender;
 
 		if (sp->voice_age != 0)
 	if (v_id == NULL)
 		return "default";
 
-	if ((strchr(v_id, '+') == NULL) && ((voice_select.gender == 0) || (voice_select.gender == base_voice.gender)) && (base_voice_variant_name[0] != 0)) {
+	if ((strchr(v_id, '+') == NULL) && ((voice_select.gender == ENGENDER_UNKNOWN) || (voice_select.gender == base_voice.gender)) && (base_voice_variant_name[0] != 0)) {
 		// a voice variant has not been selected, use the original voice variant
 		sprintf(buf, "%s+%s", v_id, base_voice_variant_name);
 		strncpy0(voice_name, buf, sizeof(voice_name));
 	SSML_STACK *ssml_sp;
 
 	static const MNEM_TAB mnem_gender[] = {
-		{ "male", 1 },
-		{ "female", 2 },
-		{ "neutral", 3 },
-		{ NULL, 0 }
+		{ "male", ENGENDER_MALE },
+		{ "female", ENGENDER_FEMALE },
+		{ "neutral", ENGENDER_NEUTRAL },
+		{ NULL, ENGENDER_UNKNOWN }
 	};
 
 	if (tag_type & SSML_CLOSE) {

src/libespeak-ng/voices.c

 #include "translate.h"
 
 MNEM_TAB genders[] = {
-	{ "male", 1 },
-	{ "female", 2 },
-	{ NULL, 0 }
+	{ "male", ENGENDER_MALE },
+	{ "female", ENGENDER_FEMALE },
+	{ NULL, ENGENDER_UNKNOWN }
 };
 
 int tone_points[12] = { 600, 170, 1200, 135, 2000, 110, 3000, 110, -1, 0 };
 			score += 400;
 	}
 
-	if (((voice_spec->gender == 1) || (voice_spec->gender == 2)) &&
-	    ((voice->gender == 1) || (voice->gender == 2))) {
+	if (((voice_spec->gender == ENGENDER_MALE) || (voice_spec->gender == ENGENDER_FEMALE)) &&
+	    ((voice->gender == ENGENDER_MALE) || (voice->gender == ENGENDER_FEMALE))) {
 		if (voice_spec->gender == voice->gender)
 			score += 50;
 		else
 			score -= 50;
 	}
 
-	if ((voice_spec->age <= 12) && (voice->gender == 2) && (voice->age > 12))
+	if ((voice_spec->age <= 12) && (voice->gender == ENGENDER_FEMALE) && (voice->age > 12))
 		score += 5; // give some preference for non-child female voice if a child is requested
 
 	if (voice->age != 0) {
 		if (vp != NULL) {
 			voice_select2.languages = &(vp->languages[1]);
 
-			if ((voice_select2.gender == 0) && (voice_select2.age == 0) && (voice_select2.variant == 0)) {
+			if ((voice_select2.gender == ENGENDER_UNKNOWN) && (voice_select2.age == 0) && (voice_select2.variant == 0)) {
 				if (variant_name[0] != 0) {
 					sprintf(voice_id, "%s+%s", vp->identifier, variant_name);
 					return voice_id;
 	}
 
 	gender = 0;
-	if ((voice_select2.gender == 2) || ((voice_select2.age > 0) && (voice_select2.age < 13)))
-		gender = 2;
-	else if (voice_select2.gender == 1)
-		gender = 1;
+	if ((voice_select2.gender == ENGENDER_FEMALE) || ((voice_select2.age > 0) && (voice_select2.age < 13)))
+		gender = ENGENDER_FEMALE;
+	else if (voice_select2.gender == ENGENDER_MALE)
+		gender = ENGENDER_MALE;
 
 	#define AGE_OLD 60
 	if (voice_select2.age < AGE_OLD)
 		// is the main voice the required gender?
 		skip = 0;
 
-		if ((gender != 0) && (vp->gender != gender))
+		if ((gender != ENGENDER_UNKNOWN) && (vp->gender != gender))
 			skip = 1;
 		if ((ix2 == 0) && aged && (vp->age < AGE_OLD))
 			skip = 1;