I'm new at C coming from java but I'm learning it in one of my college classes and so far it's a nightmare anytime I write a program with it :'(. I'm writing a Reverse polish notation calculator and I'm using gcc as my compiler. I want to be able to test it by doing this.
gcc - std=c99 -o test test.c
./test "10 7 +"
output>
strPointer 10 7 +
The result is : 17
(I'm having it display strPointer in the calculate() method to debug this issue)
but when I do the above(.test "10 7 +" )with my program below as is:
output>
strPointer 10 7 +
then it's done
if I don't use quotes, strPointer only displays 10
However....
if I uncomment this line at the very bottom
//fgets(argv[1],50,stdin);this is what happens:
./test "10 7 +" (with or without quotes this time, it doesn't matter)
output>
(blank prompt so I input)
10 7 +
then it displays
strPointer 10 7 +
The result is: 17
which is what I want
HOWEVER if just do
./test (no argument this time)
output>
(blank prompt so I input)
10 7 +
then it displays
strPointer 10 7 +
Segmentation fault
so StrPointer is getting what it's suppose to get but the segmentation fault comes out
of nowhere. Earlier on it wouldn't even display that, it would just terminate
What's the deal?
All I want is to be able to do ./test 10 7 + (with or without quotes) after compilation
I can't seem to get this working using argv[1] but the program works with fgets().
I'm required to use argv[] to do the above so I can't just ignore it, what's wrong and
how can I fix it?
It seems like my calculate() method is having a hard time using argv[1]..why?
here's my code:
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <ctype.h>
#include <stdbool.h>
typedef struct node
{
int numdata;
struct node * nextnode;
} node;
static node *top = NULL; //may not be static...not sure
node * peek(node * stack)
{
stack = top;
return stack;
}
bool Is_empty(node * stack)
{
return peek(stack) == NULL;
}
node * push(node * stack, int number)
{
static node * newItem;
newItem = calloc(sizeof(node), 1);
newItem -> numdata = number;
newItem -> nextnode = stack;
return newItem;
}
node * pop(node * stack)
{
static node * temp;
temp = stack -> nextnode;
free(stack);
return temp;
}
void clear(void)//node * stack)
{
while(top != NULL)
{
top = pop(top);
/*
while(!is_empty(stack))
{
pop(stack);
}
*/
}
}
void calculate(char * inString)
{
char * strPointer = inString;
printf("strPointer %s \n", strPointer);
char numStringordering[20];
int currentNum;
int numLength;
int assigned = 0;
top = NULL;
if (strPointer[0] == '\n')
{
return;
}
while (strPointer[0] != '\0')
{
if (isdigit(strPointer[0]))
{
numLength = strspn(strPointer,"0123456789");
if (assigned)
{
top = push(top, currentNum);
}
else
{
assigned = 1;
}
strncpy(numStringordering, strPointer, numLength);
numStringordering[numLength] = '\0';
currentNum = atoi(numStringordering);
strPointer += numLength;
}
else
{
switch (strPointer[0])
{
case '+':
{
if (top != NULL)
{
currentNum += top -> numdata;
top = pop(top);
}
else
{
printf("Error! Too many operations.\n");
return;
}
}
break;
case '-':
{
if (top != NULL)
{
currentNum = top -> numdata - currentNum;
top = pop(top);
}
else
{
printf("Error! Too many operations.\n");
return;
}
}
break;
case '*':
{
if (top != NULL)
{
currentNum *= top -> numdata;
top = pop(top);
}
else
{
printf("Error! Too many operations.\n");
return;
}
}
break;
case '/':
{
if (top != NULL)
{
currentNum = top -> numdata/currentNum;
top = pop(top);
}
else
{
printf("Error! Too many operations.\n");
return;
}
}
break;
case ' ':
break;
case '\n':
{
if (top == NULL)
{
printf("The result is: %d. \n", currentNum);
return;
}
else
{
printf("Error! Too many numbers.\n");
clear();
return;
}
}
default:
{
printf("Error! Illegal input.\n");
clear();
return;
}
}
strPointer++;
}
}
return;
}
int main(int argc, char*argv[])
{
//printf("Please input a polish postfix expression.\n\n> ");
//fgets(argv[1],50,stdin);
calculate(argv[1]);
}