printf not printing value of a character array in C

Question

The printf statement within the pop function isn't printing anything except a blank character (space). I tried to print the indexes of the array passed in the pop function but the same thing is happening. I can't seem to figure out why, can someone please help me?

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

char stack[400] = "";
int top = -1;

void push(char arr[], int *top, char val) {
    *top = *top + 1;
    arr[*top] = val;
    //printf("%d", *top);
} 

char pop(char arr[], int *top) {
    char temp;
    printf("\n%s\n", arr[0]);
    temp = arr[*top];
    *top = *top - 1;
    return temp;
}

int main() {
    push(stack, &top, 'a');
    push(stack, &top, 'b');
    push(stack, &top, 'c');
    //printf("%s", stack);
    pop(stack, &top);
    //printf("\n%s", *val);
    return 0;
}

Answer 1

If you want to print individual stack elements, you can use %d or %c like this:

char val = pop(stack, &top);
printf("stack top was %c (ASCII %d)\n", val, val);

If you want to print the whole stack as a string, you can use:

printf("stack: %.*s\n", top + 1, stack);

Note that since stack and top are passed as arguments, there is no need to make them global variables.

Here is a modified version:

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

#define STACK_DEPTH  400

void push(char arr[], int *top, char val) {
    if (top < STACK_DEPTH - 1) {
        *top = *top + 1;
        arr[*top] = val;
    } else {
        fprintf(stderr, "stack full for '%c'\n", val);
    }
} 

char pop(char arr[], int *top) {
    if (top >= 0) {
        char temp = arr[*top];
        *top = *top - 1;
        return temp;
    } else {
        fprintf(stderr, "stack empty\n");
        return 0;
    }
}

int main() {
    char stack[STACK_DEPTH] = "";
    int top = -1;

    push(stack, &top, 'a');
    push(stack, &top, 'b');
    push(stack, &top, 'c');
    printf("stack contents: %.*s\n", top + 1, stack);

    char val = pop(stack, &top);
    printf("stack top was %c (ASCII %d)\n", val, val);
    return 0;
}