Cでstackを作ります

stack.cpp

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

struct CharStack {
    char* data;
    int top; // 半開区間で終端を管理する
    int max;
} typedef stack;

void push(char* data, char c, int* top) {
    data[(*top)] = c;
    (*top)++;
}

char pop(char* data, int* top) {
    if(!(*top)) {
        return -1;
    }
    (*top)--;
    char res = *(data+(*top));
    return res;
}

void print(char* data, int* top) {
    for(int i = 0; i < *top; i++) {
        printf("%c ", data[i]);
    }
    printf("\n");
}

int main(void) {
    stack s;
    s.max = 100;
    s.top = 0;
    s.data = malloc(s.max * sizeof(*s.data));

    char input[100];
    printf("please input: ");
    scanf("%s", input);
    for(int i = 0; i < strnlen(input, 100); i++) {
        push(s.data, input[i], &s.top);
    }

    printf("pop: %c\n", pop(s.data, &s.top));
    printf("pop: %c\n", pop(s.data, &s.top));
    printf("pop: %c\n", pop(s.data, &s.top));

    printf("please input: ");
    scanf("%s", input);
    for(int i = 0;i < strnlen(input, 100); i++) {
        push(s.data, input[i], &s.top);
    }

    printf("print: ");
    print(s.data, &s.top);
}