#include <stdio.h>
#include <ctype.h>

void otog(void), gtoo(void); // ounce to grams, grams to ounce
char menu(void);

int main(void) {
  float grams;
  int ounces;
  char ch='\0';

  while(toupper(ch)!='Q') {
        if(ch!='\r') ch=menu();
        else ch='\0';
        printf("\n");
  }

  return 0;
}

void otog(void) {
  float grams;
  int ounces;

  printf("Input amount in Ounces:");
  scanf("%i",&ounces);
  grams = ounces * 28.35;
  printf("\n\nGrams: %.2f\n",grams);
}

void gtoo(void) {
  float ounces;
  int grams;

  printf("Input amount in Grams:");
  scanf("%i",&grams);
  ounces = grams * 0.0353;
  printf("\n\nOunces: %.8f\n",ounces);
}

char menu(void) {
  int good=0;
  char ch='\0',garbage;

  printf("1.) Convert Ounces to Grams\n");
  printf("2.) Convert Grams to Ounces\n");
  printf("Q.) Quit\n");
  printf("===========================\n");
  printf(" Selection: ");
  scanf("%c%c",&ch,&garbage);

 /* Garbage will absorb the enter */

  if(garbage!='\n') ch=garbage;

  if(ch=='1') {
    otog();
    good=1;
    ch='1';
  }
  if(ch=='2') {
    gtoo();
    good=1;
  }

  if(good==0) return('Q');
  else return(ch);
}

#define G_FOR_OZ 28.349

float ouncesToGrams(float ounces) { return ounces * G_FOR_OZ; }
float gramsToOunces(float grams) { return grams / G_FOR_OZ; }

printf("Input amount in Grams:");
scanf("%f",&grams);
printf("\n\nOunces: %.8f\n", gramsToOunces(grams) );