Stack calculator altering the value of a variable - c

Question

For my programming class I have to program a calculator that functions with a stack.
Here's the code I made for the stack itself:
#include <stdio.h>
#include <stdlib.h>
#define MAXSIZE 10
double stk[MAXSIZE]; //Stack array
int top=-1; //Top position in stack
void push(double n);
double pop(void);
void display(void);
/* Add an element to the stack */
void push(double n) {
if (top == (MAXSIZE - 1)) {
printf ("Stack is full\n");
}
else {
//s.top++;
//stk = (double *) malloc(MAXSIZE*sizeof(double));
stk[++top] = n;
}
return;
}
/* Remove and return the top element from the stack */
double pop() {
double num;
if (top == -1) {
printf ("Stack is empty\n");
return (top);
}
else {
num = stk[top--];
printf ("Pop:%f\n", num); //Debugging line
return (num);
}
}
/* Prints all elements in the stack */
void display() {
int i;
if (top == -1) {
printf ("Stack is empty\n");
return;
}
else {
for (i = top; i >= 0; i--) {
printf ("%f\n", stk[i]);
}
}
}
And this is the the calculator (which is in a different file, I'm using makefile to compile):
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <ctype.h>
#include <math.h>
int isNumber(const char *s);
void insert(double num);
void sum(void);
int main(int argc, char *argv[]) {
int loop = 1;
char input[10];
/* Main Loop */
while (loop == 1) {
printf("> ");
scanf(" %[^\n]", input);
if (isNumber(input)) {
double nu = atof(input);
insert(nu);
}
else if (strcmp(input, "+") == 0)
sum();
else if (strcmp(input, "l") == 0)
list();
else if (strcmp(input, "exit") == 0) //exit
loop = 0;
} //end while
} //end main
int isNumber(const char *s) {
while (*s) {
if((*s<'0' || *s>'9') && *s!='-' && *s!='.')
return 0;
s++;
}
return 1;
}
void insert(double num) {
push(num);
}
/* This function is called when the user enters a '+' instead of a number into the command line. It takes the top two numbers from the stack and adds them together */
void sum() {
double num1, num2, res;
num1 = pop();
num2 = pop();
res = num1+num2;
printf("num1:%f num2:%f sum:%f\n", num1, num2, res); //Debug
}
int list() {
display();
}
The program compiles fine. When I run it I test it by entering a 5 followed by a 6 followed by a + and I get this output:
Pop:6.000000
Pop:4.000000
num1:13.000000 num2:13.000000 sum:26.000000
So apparently the number that the pop() function returns is correct but when assigning it to variables in the calculator function it changes it into a 13 for some reason. It's not always 13, for larger numbers it's higher; entering 500 returns 14, 1000 returns 15, 10000 returns 16 and so on.
I initially made my stack with a array of ints and it actually worked perfectly (it still does if I change all the doubles to ints). Also the stack itself seems to be working fine since the display() function correctly prints all the values the user entered).
I'm really confused as to where the error is coming from and I'm actually thinking of rewriting the whole stack as a linked list instead but I wanted to give this a last shot.
Thanks in advance for your help.
EDIT: I added an #include "Stack.h" (Changed Stack.c to Stack.h) in my calculator file and disposed of the makefile and it now works. I have no idea what was happening originally but I'm just glad it works.

Answer 1

I put all your logic in one file, and add simple main:
int main()
{
push(4.0);
push(3.8);
sum();
return 0;
}
Then compile all as gcc main.c. And it works fine:
Pop:3.800000
Pop:4.000000
num1:3.800000 num2:4.000000 sum:7.800000
Are you sure that you really normally link your project (and break your code to some modules)? Can you put more information about how you compile your version?
P.S. You have all good in program logic
Update
You need to add Stack.h file with the same text:
#include <stdio.h>
#include <stdlib.h>
void push(double n);
double pop(void);
void display(void);
In Stack.c remove this code and add #include "Stack.h" in the first line.
In Main.c only add #include "Stack.h" in the 6 line (just after system #include directives).
Don't change your makefile. It's not required.
With regards,
AJIOB