Access Violation Reading Loaction 0x00000000 in C

[FaiL___]

Hi, I'm meant to be basically making a calculator, but for some reason, it keeps saying this error message. The code is breaking on this line: 

if (strcmp((operatorSymbol, "*") == 0))

Thanks in advance for helping, if you could a) fix it, b) explain to me why it is doing this so I can learn, that'd be great. TY

[FaiL___]

Just now, Nicholatian said:

Show us the full code. AFAICS operatorSymbol is undefined, which means it shouldn’t even compile.

Full code is: 

#include <stdio.h>

#pragma warning(disable: 4996)

int main(int argc, char *argv[])
{
	float numberOne = 0, numberTwo = 0, answer = 0;
	char operatorSymbol[1];
	int numberOfValuesRead = 0;


	if (argc == 4)
	{
		sscanf(argv[2], "%s", &operatorSymbol);
		numberOfValuesRead = sscanf(argv[1], "%f", &numberOne);
		if (numberOfValuesRead == 1)
		{
			numberOfValuesRead = sscanf(argv[3], "%f", &numberTwo);
			if (numberOfValuesRead == 1)
			{
				if (strcmp((operatorSymbol, "*") == 0))
				{
					answer = numberOne * numberTwo;
					printf("%f", answer);
				}
				else if (strcmp((operatorSymbol, "/") == 0))
				{
					if (numberTwo == 0)
					{
						printf("invalid output");
					}
					else
					{
						answer = numberOne / numberTwo;
						printf("%f", answer);
					}
				}
				else if (strcmp((operatorSymbol, "+") == 0))
				{
					answer = numberOne + numberTwo;
					printf("%f", answer);
				}
				else if (strcmp((operatorSymbol, "-") == 0))
				{
					answer = numberOne - numberTwo;
					printf("%f", answer);
				}
			}
			else
			{
				printf("invalid input");
			}
		}
		else
		{
			printf("invalid input");
		}

	}
	getchar();
}

 

[Unimportant]

53 minutes ago, FaiL___ said:

Hi, I'm meant to be basically making a calculator, but for some reason, it keeps saying this error message. The code is breaking on this line: 

if (strcmp((operatorSymbol, "*") == 0))

Thanks in advance for helping, if you could a) fix it, b) explain to me why it is doing this so I can learn, that'd be great. TY

You're not calling 'strcmp' the way you think you're calling it, this is the declaration for 'strcmp':

int strcmp ( const char * str1, const char * str2 );

It wants 2 const char pointers as parameters.

 

What are you calling ?

strcmp(       (operatorSymbol, "*") == 0          )

Which decomposes to:

strcmp(   "*" == 0     )

 

Which will always result in:

strcmp(    0    )

So, you're calling:

int strcmp ( int );

A function that was not declared. If you turn up your compiler warnings (or read them in the first place) you should've received a warning along the lines of "implicit declaration of function".

 

Older C standards allowed to call functions that were not declared yet, resulting in a implicit declaration. However the implicitly declared 'strcmp' does not match the real 'strcmp', the parameters don't match at all, and thus you invoke undefined behavior.

[bcguru9384]

On ‎10‎/‎9‎/‎2017 at 10:29 AM, FaiL___ said:

Hi, I'm meant to be basically making a calculator, but for some reason, it keeps saying this error message. The code is breaking on this line: 

if (strcmp((operatorSymbol, "*") == 0))

Thanks in advance for helping, if you could a) fix it, b) explain to me why it is doing this so I can learn, that'd be great. TY

if strcmp ( ( operatorsymbol, "*") == 0)

note spaces as space gives system place to place + or - for indicating if neg # or pos #

if space then pos

if - then neg

space has to be there ( #) or (-#)

if ( used then followed by space or - then # then closed )