How to format command line input in C

Question

I'm trying to do the parentheses balance problem and adjust the following code to work with command-line input (argc/argv), but I can't figure out how to properly push variables to the stack and do comparisons between the stack and parentheses.

balance.c: In function 'push':
balance.c:16:18: error: expected expression before 'char'
     len = strlen(char[i]);
                  ^~~~
balance.c:19:9: error: expected expression before 'char'
         char[i]=other[i];
         ^~~~
balance.c:25:22: warning: assignment makes integer from pointer without a cast [-Wint-conversion]
         s.stk[s.top] = other;
                      ^
balance.c: In function 'main':
balance.c:55:33: warning: comparison between pointer and integer
                 if(s.stk[s.top] == "(")

I was hoping to get advice on how to properly format cmd input so I would be able to make comparisons. I've adjusted some of them by using strcmp, but am not sure how to move forward.

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#define MAX 20

struct stack
{
    char stk[MAX];
    int top;
}s;

void push(char* item)
{
    int len;
    int i;
    len = strlen(char[i]);
    char other [len];
    for(i=0;i<len;i++)
        char[i]=other[i];
    if (s.top == (MAX - 1))
        printf ("Stack is Full\n");
    else
    {
        s.top = s.top + 1; // Push the char and increment top
        s.stk[s.top] = other;
    }}

void pop()
{
    if (s.top == - 1)
    {
        printf ("Stack is Empty\n");
    }
    else
    {
        s.top = s.top - 1; // Pop the char and decrement top
    }}

int main(int argc, char* argv[])
{
    int i = 0;
    s.top = -1;
    for(i = 0;i < argc;i++)
    {
        if((strcmp(argv[i],"(")==0) || (strcmp(argv[i],"[")==0) || (strcmp(argv[i],"{")==0))
        {
            push(argv[i]); // Push the open bracket
            continue;
        }
        else if((strcmp(argv[i],")")==0) || (strcmp(argv[i],"]")==0) || (strcmp(argv[i],"}")==0)) // If a closed bracket is encountered
        {
            if((strcmp(argv[i],")")==0))
            {
                if(s.stk[s.top] == "(")
                {
                    pop(); // Pop the stack until closed bracket is found
                }
                else
                {
                    printf("\nUNBALANCED EXPRESSION\n");
                    break;
                }}
            if((strcmp(argv[i],"]")==0))
            {
                if(s.stk[s.top] == "[")
                {
                    pop(); // Pop the stack until closed bracket is found
                }
                else
                {
                    printf("\nUNBALANCED EXPRESSION\n");
                    break;
                }}
            if((strcmp(argv[i],"}")==0))
            {
                if(s.stk[s.top] == "{")
                {
                    pop(); // Pop the stack until closed bracket is found
                }
                else
                {
                    printf("\nUNBALANCED EXPRESSION\n");
                    break;
                }}}}
    if(s.top == -1)
    {
        printf("\nBALANCED EXPRESSION\n"); // Finally if the stack is empty, display that the expression is balanced
    }}

Answer 1

Problems:

len = strlen(char[i]);
Does not mean nothing. If you want to get the size of item, you must write:
len = strlen(item);

---

char other [len];
for(i=0;i<len;i++)
    char[i]=other[i];

You try to copy the uninitiated data of other into...item? In that case, you should have written

char other [len+1];
for(i=0;i<len;i++)
    other[i] = item[i];
other[len] = '\0'; // do not forget the final character of a NULL terminated string.

or

char other [len+1];
strcpy(other, item);

But, since other will be use in the stack, so outside of push, it can't be internal to push, you have to reserve some memory with malloc or friend functions. In that case, you don't need len and a simple

char *other = strdup(item); //( ~ malloc + strcpy in one function)

whould be enough.

(re)But given the stack and the code using it, it seems you only stack single characters. In that case, you could simplify push to:

void push(char* item)
{
    if (s.top == (MAX - 1))
        printf ("Stack is Full\n");
    else
    {
        s.top = s.top + 1; // Push the char and increment top
        s.stk[s.top] = item[0]; 
    }
}

---

On one other side, your main function seems complicated using strcmp where simple char comparison would suffice:

(strcmp(argv[i],"(")==0)

can be written

( argv[i][0] == '(' )

And you stack character checking is wrong:

            if(s.stk[s.top] == "(")

should be writteng

            if(s.stk[s.top] == '(')

Moreover, your code could have a real interest using switch/case:

int main(int argc, char* argv[])
{
    int i = 0;
    s.top = -1;
    for(i = 0;i < argc;i++)
    {
        switch(argv[i][0]) {
            case '(':
            case '[':
                push(argv[i]); // Push the open bracket
                break;
            case ')':
                if(s.stk[s.top] == '(') // note what happend in s.top is -1?
                    pop()
                else
                    printf("\nUNBALANCED EXPRESSION\n");
                    return;
            case ']':
                if(s.stk[s.top] == ']') // note what happend in s.top is -1?
                    pop()
                else
                    printf("\nUNBALANCED EXPRESSION\n");
                    return 0;

        }
    }
       
    if(s.top == -1)
    {
        printf("\nBALANCED EXPRESSION\n"); // Finally if the stack is empty, display that the expression is balanced
    }
    return 0;
}