Implement prompt function

include/amadeus/prompt.h

@@ -1,5 +1,6 @@
 #ifndef PROMPT_H
 #define PROMPT_H
 
+int prompt(const char **message);
 
 #endif // PROMPT_H

src/prompt.c

@@ -0,0 +1,29 @@
+#include <AMaDEUS/prompt.h>
+
+#include <stdio.h>
+#include <stdlib.h>
+
+int prompt_counted(const char **message, int count);
+
+int prompt(const char **message) {
+    return prompt_counted(message, 0);
+}
+
+int prompt_counted(const char **message, int count) {
+    printf("%s: ", *message);
+
+    char *buffer = NULL;
+    size_t buffer_size = 0;
+    getline(&buffer, &buffer_size, stdin);
+
+    int result = atoi(buffer);
+    if (result != 0) {
+        return result;
+    } else if (++count < 3) {
+        printf("Invalid input. Please try again.\n");
+        return prompt_counted(message, count);
+    } else {
+        printf("Too many invalid inputs. Exiting.\n");
+        exit(1);
+    }
+}