How to return a variable name and assign the value of the variable returned in c

The simple answer here is that this is not possible in C.

The longer answer is that this requires introspection and dynamic features in a language, which is something that is generally only seen in scripting languages such as Python. And even there doing something like this is not encouraged.

I suggest that you reconsider the problem you are trying to solve and check if there might not be a better method to approach it. Perhaps using an array, map or hash table might be an alternative approach that works for you.

C is not a dynamic language - you can't really do this. You'd just better use some kind of data structure, such as a dictionary (key-value store, associative array, however you call it) for this purpose.

Well, unless... unless you have a POSIX-conformant system and you like evil dynamic loading.

#include <dlfcn.h>
#include <stdio.h>

int globalVarOne = 1;
int globalVarTwo = 2;
int globalVarThree = 3;

int getValueOfVariableNamed(const char *name)
{
    void *ptr = dlsym(RTLD_SELF, name);
    return *(int *)ptr;
}

int main()
{
    printf("globalVarOne = %d\n", getValueOfVariableNamed("globalVarOne"));
    // etc.
}

Prints:

globalVarOne = 1

Note that this only works for global variables.

Edit: as @oldrinb pointed out, you can also do this on Windows if you substitute void *ptr = GetProcAddress(GetModuleHandle(NULL), name); instead of void *ptr = dlsym(RTLD_SELF, name);.

You can't do it directly in C.

You can do something like this however:

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

typedef struct Binding
{
  int* pIntVar;
  const char* IntVarName;
  struct Binding* pNext;
} Binding;

Binding* Bindings = NULL;

void BindVar(const char* IntVarName, int* pIntVar)
{
  Binding* b;
  if ((b = malloc(sizeof(Binding))) != NULL)
  {
    b->IntVarName = IntVarName;
    b->pIntVar = pIntVar;
    b->pNext = NULL;
    if (Bindings == NULL)
    {
      Bindings = b;
    }
    else
    {
      Binding* bs = Bindings;
      while (bs->pNext != NULL)
      {
        bs = bs->pNext;
      }
      bs->pNext = b;
    }
  }
  else
  {
    fprintf(stderr, "malloc() failed\n");
    exit(-1);
  }
}

int* GetVarPtr(const char* IntVarName)
{
  Binding* bs = Bindings;
  while (bs != NULL)
  {
    if (!strcmp(bs->IntVarName, IntVarName))
    {
      return bs->pIntVar;
    }
    bs = bs->pNext;
  }
  fprintf(stderr, "variable \"%s\" not bound yet!\n", IntVarName);
  exit(-1);
}

int main(void)
{
  int ABC = 111, DEF = 222, XYZ = 333;
  const char* varName = NULL;

  BindVar("ABC", &ABC);
  BindVar("DEF", &DEF);
  BindVar("XYZ", &XYZ);

  printf("variable \"%s\" = %d\n", "ABC", *GetVarPtr("ABC"));
  printf("variable \"%s\" = %d\n", "DEF", *GetVarPtr("DEF"));
  printf("variable \"%s\" = %d\n", "XYZ", *GetVarPtr("XYZ"));

  // Pick a variable randomly by name

  switch (rand() % 3)
  {
  case 0: varName = "ABC"; break;
  case 1: varName = "DEF"; break;
  case 2: varName = "XYZ"; break;
  }

  printf("variable \"%s\" (selected randomly) = %d\n", varName, *GetVarPtr(varName));

  return 0;
}

Output (ideone):

variable "ABC" = 111
variable "DEF" = 222
variable "XYZ" = 333
variable "DEF" (selected randomly) = 222

Since GetVarPtr() returns a pointer to a variable, you can not only get the variable's value, but also set it.

You can even hide the pointer thing behind a macro:

#define VARIABLE(NAME) (*GetVarPtr(NAME))

In this way you can do things like this (ideone):

VARIABLE("ABC") = 1;
VARIABLE("DEF") = 2;
VARIABLE("XYZ") = 3;

printf("variable \"%s\" = %d\n", "ABC", VARIABLE("ABC"));
printf("variable \"%s\" = %d\n", "DEF", VARIABLE("DEF"));
printf("variable \"%s\" = %d\n", "XYZ", VARIABLE("XYZ"));

You can't use macros during runtime.

You should use an array.