RPN计算器程序出错C

Question

我正在创建一个反向抛光表示法计算器，它还可以使用argv[]输入选项来执行其他一些操作。但是现在，我只有RPN计算器选项，我得到一个奇怪的错误，我需要帮助。

我收到错误：

Undefined                       first referenced
symbol                          in file
fmod                            /var/tmp//ccGTG20S.o
ld: fatal: Symbol referencing errors. No output written to project
collect2: ld returned 1 exit status

这是我的代码：

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

void push(float stack[], float value, int *currStack)
{
  int i = *currStack;

  while (i != 0)
    {
      stack[i] = stack[i-1];
      i--;
    }

  stack[0] = value;
  *currStack += 1;
}

void pop(float stack[], char operation, int *currStack)
{
  int i;

  switch (operation)
    {
    case 'A':
      stack[0] = stack[1] + stack[0];
      break;
    case 'S':
      stack[0] = stack[1] - stack[0];
      break;
    case 'X':
      stack[0] = stack[1] * stack[0];
      break;
    case 'D':
      stack[0] = stack[1] / stack[0];
      break;
    case 'M':
      stack[0] = fmod(stack[1], stack[0]);
      break;
    default:
      printf("error: the symbol %c is neither a supported operator nor an integer\n", operation);
      break;
    }

  for (i=1;i<*currStack;i++)
    {
      stack[i] = stack[i+1];
    }
  *currStack -= 1;
}

void decode(char **instring, float *outval, int size)
{
  int i=0, currStack=0;
  float stack[size/2];

  for (i=1;i<size;i++)
  {
      if (atof(instring[i]))
        push(stack, atof(instring[i]), &currStack);
        else
          pop(stack, *instring[i], &currStack);

      *outval = stack[0];
    }
}

int evaluate(int argc, char *argv[])
{
  float result;
  decode(argv, &result, argc);

  printf("%.2f\n", result);

  return 0;
}

int
main(int argc, char *argv[])
{

  if( (argc>1 )&&(strcmp(argv[1],"-e")!=0) && (strcmp(argv[1],"-c")!=0) && (strcmp(argv[1],"-g")!=0)){
    fprintf(stderr, "%s: option %s is unsupported\n", argv[0], argv[1]);
  }
  if ((argc>1) && strcmp(argv[1], "-e")==0)
    {
      evaluate(argc, argv);
    }
  else if ((argc>1) && strcmp(argv[1],"-c")==0)
    {

    }
  else if ((argc>1) && strcmp(argv[1],"-g")==0)
    {

    }
  return EXIT_SUCCESS;
}