C program, Stack Calculator [closed] - c

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Closed 10 years ago.
Can someone please take a look at my code below and help me out. Ive been trying to fix this for hours but i cant figure out what's wrong. It's a program written in C that is supposed to take the operations of a stack calculator and store the operands of a mathematical expression. When an operation is performed, the last two values on the stack are removed and used as the operands, then the result of the operation is placed on the stack. However, I'm not getting the right numbers. Please take a look at my code. I know it's long, but I appreciate it. Thanks.
#include <stdio.h>
#include <string.h>
#include <math.h>
#include <stdlib.h>
#define SIZE 10
#define MAXINPUT 255
void printStack(int stack[], int tos)
{
if (isEmpty(tos))
{
printf("Stack is empty\n");
printf("---------------------------------------\n");
return;
}
printf("Stack: ");
while (tos < SIZE)
{
printf("[%d] " , stack[tos]);
tos++;
}
printf("\n---------------------------------------\n");
}
int top (int stack[], int tos)
{
if(isEmpty(tos))
return;
return stack [tos];
}
int isEmpty(int tos)
{
if (tos < 0)
return 1;
}
int isFull (int tos)
{
if(tos >= SIZE - 1)
return 1;
}
void push(int val, int stack [], int *tos)
{
if(isFull(*tos))
return;
(*tos)++;
stack[*tos] = val;
}
int pop (int stack [], int *tos)
{
if(isEmpty(*tos))
return;
int val = stack[*tos];
(*tos)--;
return val;
}
void clear(int *tos)
{
*tos = -1;
}
int getInput (char *input)
{
printf("+------------------------------{Choose an option}------------------------------+\n");
printf("| (q) : quit the program. |\n"
"| (integer value) : an integer value (either positive or negative) to push |\n"
"| (c) : clear the stack |\n"
"| (=) : display top value on the stack |\n"
"| (+) : addition |\n"
"| (-) : subtraction |\n"
"| (*) : multiplication |\n"
"| (/) : division - integer division only |\n"
"| (%) : modulus - remainder from an integer division |\n"
"| (^) : exponentiation (x raised to the power of y) |\n"
"+------------------------------------------------------------------------------+\n");
printf("Input: ");
gets(input);
if(strcmp(input, "q") == 0)
{
printf("Exiting...\n");
return 0;
}
return 1;
}
int isNum(char *input)
{
int i;
for(i = 0; i < strlen(input); i++)
{
if(!isdigit(input[i]))
return 0;
}
return 1;
}
int hasTwo(tos)
{
if((SIZE - tos) >= 2)
return 1;
printf("\nStack size is 1, must have 2 or more\n");
return 0;
}
void mathOp (char op, int stack[], int *tos)
{
if(!isEmpty(*tos))
return;
if(!hasTwo(*tos))
return;
int right = pop(stack, tos);
int left = pop(stack, tos);
switch(op)
{
case '+':
push((left + right), stack, tos);
break;
case '-':
push((left - right), stack, tos);
break;
case '*':
push((left * right), stack, tos);
break;
case '/':
push((left/right), stack, tos);
break;
case '%':
push((left % right), stack, tos);
break;
case '^':
push(pow(left, right), stack, tos);
break;
}
}
int main(int argc, char **argv)
{
int verbose = 0;
int debugMode = 0;
if (argc == 2 && argv[1][0] == '-' && argv[1][1] == 'd')
{
debugMode = 1;
if (strcmp("-dv", argv[1]) == 0)
{
verbose = 1;
}
}
int stack[SIZE];
int tos = -1;
char input[MAXINPUT];
while (getInput(input))
{
int result = 0;
if (strcmp(input, "c") == 0)
clear(&tos);
else if (strcmp(input, "=") == 0)
{
result = top(stack, tos);
printf("Top of Stack is [%d]\n", result);
}
else if (isNum(input))
push(atoi(input), stack, &tos);
else if(strcmp(input, "+") == 0 ||
strcmp(input, "-") == 0 ||
strcmp(input, "*") == 0 ||
strcmp(input, "/") == 0 ||
strcmp(input, "%") == 0 ||
strcmp(input, "^") == 0 ) mathOp(input[0], stack, &tos);
else
printf("Invalid input\n");
if (debugMode)
printStack(stack, tos);
}
return 0;
}

Answer 1

You have a lot of problems in this code. Compile with -Wall (or equivalent setting) to find that isEmpty and isFull and top and pop don't (always) properly return a value.
Every function that needs to return something, must end in a return statement. There is no 'default return value' of some sorts in C.
So as an example:
int isFull (int tos)
{
if(tos >= SIZE - 1)
return 1;
return 0; // <-- not full, you probably want to return 0
}
ps. You need to use %% for a literal % in the help text.
edit to fix everything:
printStack is badly broken, you need to loop from 0 to tos, not from tos to SIZE.
hasTwo needs to test if tos>=1.
mathOp needs to test first if(isEmpty(*tos)), remove the ! which says not "if not empty".
Then it should work.