Why doesn't my "SaveToMemory" command actually save in this mixed number calculator?

 I've attempted a bunch of different iterations of this and they have all failed. Whenever you attempt to save the current value it never saves. When you go to try to use 'GetFromMemory' it instead just displays the current value instead of the saved one.

I've tried multiple iterations of and can't seem to find the problem on why it won't save.

#include <stdlib.h>
#include <stdio.h>
#include <ctype.h>
#include <string.h>
#include "Strings.h"

#include "MN.h"

#define LIMIT 32

#define WHAT '?'
#define QUIT 'Q'
#define READ 'R'
#define PRINT 'P'
#define ADD   '+'
#define SUBTRACT '-'
#define MULTIPLY '*'
#define DIVIDE '/'
#define WHOLE 'W'
#define NUM 'N'
#define DEM 'D'
#define INVERT 'I'
#define COMPARE 'C'
#define SAVE 'S'
#define GET 'G'
#define MEMORY 'M'
#define PERIOD '.'

void print(MN this) {
   printf("   %s",toStringMN(this));
}

void println(MN this) {
   print(this);
   printf("\n");
}

MN read(char *s) {
   MN result;
   char *input;
   if(Slength(s) < 1) {
      printf(" :>"); input = nextLine(LIMIT);
      result = newSMN(input);
      free(input);
   } 
   else {
      result = newSMN(s);
   }
   return result;
}

int readIndex(char *s) {
   int result;
   char *input;
   int success = 0;
   do {
      if((success == 0) || (Slength(s) < 1)) {
         printf(" :>"); input = nextLine(LIMIT);
         success = sscanf(input,"%d",&result);
         free(input);
      } 
      else {
         success = sscanf(s,"%d",&result);
      }
   } while(success < 1);
   return result;
}

int validIndex(int index) {
   int result = 0;
   if((index > 0) && (index <= LIMIT)) {
      result = index;
   }
   return result;
}

int validMemory(int index, MN memory[]) {
   int result = 0;
   if((validIndex(index) == index) && (memory[index] != NULL)) {
      result = index;
   }
   return result;
}


void printWHAT() {
   printf("   Valid Commands are:\n");
   printf("     %c=List Commands, %c=Quit, %c=Read, %c=Print,\n",
               WHAT,QUIT,READ,PRINT);
   printf("     %c=Add, %c=Subtract, %c=Multiply, %c=Divide,\n",
               ADD,SUBTRACT,MULTIPLY,DIVIDE);
   printf("     %c=Invert, %c=Whole, %c=Numerator, %c=Denominator, %c=Compare\n",
               INVERT,WHOLE,NUM,DEM,COMPARE);
   printf("     %c=SaveToMemory, %c=GetFromMemory, %c=DisplayMemory\n",
               SAVE,GET,MEMORY);
}

void nullify(MN array[]) {
   for(int i=0; i<LIMIT+1; i++) {
      array[i] = NULL;
   }
}

int main() {
   MN memory[LIMIT+1];
   nullify(memory);
   MN X = newIMN(1,0,0,1);
   MN Y;
   memory[0] = newIMN(1,0,0,1);
   char *input;
   char command;
   int toPrint;
   do {
      toPrint = 1;
      printf("::>"); input = nextLine(LIMIT);
      command = toupper(input[0]);
      if(command == WHAT) {
         printWHAT();  toPrint = 0;
      } 
      else if(command == READ) {
         X = read(input+1);
      } 
      else if(command == PRINT) {
      } 
      else if(command == ADD) {
         Y = read(input+1);  addMN(X,Y);
      } 
      else if(command == SUBTRACT) {
         Y = read(input+1);  subtractMN(X,Y);
      } 
      else if(command == MULTIPLY) {
         Y = read(input+1);  multiplyMN(X,Y);
      } 
      else if(command == DIVIDE) {
         Y = read(input+1);  divideMN(X,Y);
      } 
      else if(command == WHOLE) {
         toPrint = 0;
         printf("   %d\n",wOfMN(X));
      } 
      else if(command == NUM) {
         toPrint = 0;
         printf("   %d\n",nOfMN(X));
      } 
      else if(command == DEM) {
         toPrint = 0;
         printf("   %d\n",dOfMN(X));
      } 
      else if(command == INVERT) {
         invertMN(X);
      } 
      else if(command == COMPARE) {
         toPrint = 0;
         Y = read(input+1);
         printf("   %d\n",compareToMN(X,Y));
      } 
      else if(command == SAVE) {
         memory[validIndex(readIndex(input+1))] = X;
         }
      } 
      else if(command == GET) {
         X = memory[validMemory(readIndex(input+1),memory)];
      } 
      else if(command == MEMORY) {
         for(int i=0; i<=LIMIT; i++) {
            if(memory[i] != NULL) {
               printf("   %2d: %s\n",i,toStringMN(memory[i]));
            }
         }
      } 
      else if(command != QUIT) {
         toPrint = 0;
         printf("   --->UNKNOWN COMMAND\n");
      }
      if((command != QUIT) && toPrint) {
         println(X);
      }
      free(input);
   } while(command != QUIT);
}

For example I've tried this thinking it was a problem with setting X to the memory index if valid however it didn't solve my issue.

      else if(command == SAVE) {
         int index = readIndex(input+1);
         if(validIndex(index)) {
         
memory[index] = X;
         
}

It seems like there is an extra closing curly brace } at the end of the SAVE case, which should not be there. This causes a syntax error and the SAVE command is not properly executed. Removing the extra curly brace should fix the issue:
scss
else if(command == SAVE) {
    memory[validIndex(readIndex(input+1))] = X;
} // <-- Remove this curly brace
else if(command == GET) {
    X = memory[validMemory(readIndex(input+1),memory)];
}
With this fix, the SAVE command should correctly save the current value to memory, and the GET command should retrieve the saved value from memory.