Problem with comparing character

iblink · #1 12-Nov-2009, 08:21

Hello. I am trying to push in into a stack characters one by one from a char array. It is prompted to stop when an asterisks '*' char is read. But it doesnt seem to work that way for me. I am having problem with the part where i compare each char to '*' while(input[i] != '*'). I get no output from the program and it exits. Can someone help me with that. My program is bellow.

CPP / C++ / C Code:

#include<stdio.h>
#include<stdlib.h>
#include<ctype.h>

typedef struct 
{
    char home[35];
    int top;
} My_stack;

void push (My_stack *, char);/
void pop (My_stack *);
int is_empty (My_stack *);


int main()
{
	My_stack st;
	char input[50];   /* input sequence for processing */
	int i = 0;
	st.top = -1;

	printf("Enter the sequence : ");
	gets(input);
	
	while(input[i] != '*')   /* while '*' is not reached */
	{
		push(&st, input[i]);  /* push character onto the stack */
			
		i++;	
	}
	i =0;
	while(input[i] != '\0'){
	pop(&st);
	i++;
	}
	return 0;
}
void push(My_stack * s, char c)   // push (insert) operation
{  // assume there is enough space for pushing next element!
	s->top ++;
	s->home[s->top] = c; 
}
void pop(My_stack * s)   // pop (remove) operation
{
	if(is_empty(s))  
	{ 
		printf("ERROR: Nothing to pop - program terminates\n");
		exit(1);
	}
	printf("%c", s->home[s->top--]);
}
int is_empty(My_stack * s)   // checking whether stack is empty or not
{
	return(s->top < 0 ? 1 : 0);
}

fakepoo · #2 12-Nov-2009, 08:28

What is your intention here?

CPP / C++ / C Code:

while(input[i] != '\0'){
	pop(&st);
	i++;
	}

Also, you may want to put printf() statements throughout the code so that you can see the value of certain variables. For instance, it might be wise to print to the screen the user input that you read.

iblink · #3 12-Nov-2009, 08:35

That isn't part of the initial program. Just did that to see what i have in the stack after pushing the characters.

fakepoo · #4 12-Nov-2009, 09:11

I ran your program with printf() in it like so:

CPP / C++ / C Code:

#include<stdio.h>
#include<stdlib.h>
#include<ctype.h>

typedef struct 
{
    char home[35];
    int top;
} My_stack;

void push (My_stack *, char);
void pop (My_stack *);
int is_empty (My_stack *);


int main()
{
	My_stack st;
	char input[50];   /* input sequence for processing */
	int i = 0;
	st.top = -1;

	printf("Enter the sequence : ");
	gets(input);
	printf("Received: %s\n", input);
	
	while(input[i] != '*')   /* while '*' is not reached */
	{
		printf("input[%d]: %c\n", i, input[i]);
		push(&st, input[i]);  /* push character onto the stack */
			
		i++;	
	}
	i =0;
	while(input[i] != '\0'){
	pop(&st);
	i++;
	}
	getchar();
	return 0;
}
void push(My_stack * s, char c)   // push (insert) operation
{  // assume there is enough space for pushing next element!
	s->top ++;
	s->home[s->top] = c; 
}
void pop(My_stack * s)   // pop (remove) operation
{
	if(is_empty(s))  
	{ 
		printf("ERROR: Nothing to pop - program terminates\n");
		getchar();
		exit(1);
	}
	printf("%c", s->home[s->top--]);
}
int is_empty(My_stack * s)   // checking whether stack is empty or not
{
	return(s->top < 0 ? 1 : 0);
}

This is the output:

Code:

Enter the sequence: abc*jkl
Received: abc*jkl
input[0]: a
input[1]: b
input[2]: c
cbaERROR: Nothing to pop - program terminates

This is what I expected. Did you?

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Problem with comparing character

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