Thread: Segmentation fault on my program

I tried to run my unfinishem program and I get a segmentation fault. It compiles without errors and warnings.

Code:

//Reverse Polish Notation Calc
#include<stdio.h>
#include<stdlib.h>
#include<ctype.h>
#include<string.h>
void help();

int main(int argc, char *argv[]){
int i;
int u=0;
int j=0;
int z=0;
int st_stevk=0;
float sklad[20];
float plus[20];

      if(argc<4)
        {
          help();
	  exit(1);
	 }
	 
	 
  for(i=1;i<argc;i++)
  
   {
    if(isdigit(argv[i]))
        {
	  sklad[j]=atof(argv[i]);
	  j++;
	  st_stevk++;
    }
	  if((st_stevk>=2)&&(isalpha(argv[i])))
	   {
	     z=j-st_stevk;
	     switch(*argv[i]){ //ascii kode od operatorjev
	     
	     case '+': for(u=0;u<st_stevk;u++)
	                {
			   plus[u]=sklad[z];
			   z++;
			  
			 };
	    //case '-':  for(i=
			 
	 }
	  st_stevk=0;
	
    }

}
 return 0;
 
}
 void help() {
                  printf("\n");
   char hilfe[]="Vpisati moras vsaj tri argumente!\n" 
                "Primer: ./sedma 3 4 +, pri tem pa\n" 
	        "mora biti operator vedno za zadnjim\n"
	        "operandom, ki ga operacija zajema\n";
	          printf("%s\n",hilfe);
	    
	    }

Im trying to make a RPN calculator. That means that first the operands are inputed(im my prog as cmd arguments) and then the operator.
Example:
3 5 + would print 8 (3+5).
The reason Im complicating is because I would like to make this to work for more operands and operators:
Example :
input: 2 3 + returns 5
5 4 + returns 9
* returns 45

Anyway, can someone please explain what causes segmentation fault.

THanks!