amazon online test 2

amazon.c

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

#define MAX_INPUT_SIZE 100

int g_error = 0;

void error(const char *msg){
    /*
    printf("%s\n", msg);
    exit(-1);
    */
    g_error = 1;
}

int str_to_int(char str[], int begin, int end){
    int result = 0, i, sign = 1;
    
    i = begin;
    if(str[begin] == '+') i ++;
    if(str[begin] == '-') { sign = -1; i ++; }

    for(; i <= end; i ++){
        result *= 10;
        result += str[i] - '0';
    }
    return sign * result;
}

void op_result(char op, double *result, double a){
    if(op == '+'){
        *result = *result + a;
    } else if(op == '-'){
        *result = *result - a;
    } else if(op == '*'){
        *result = *result * a;
    } else if(op == '/'){
        *result = *result / a;
    } else {
        error("invalid operator");
    }
}

int cal(char str[], int begin, int end){
    double result = 0;
    char op;
    int i, j, p_count, is_first;

    if(str[begin] == '+' || str[begin] == '-' || (str[begin] >= '0' && str[begin] <= '9')){
        return str_to_int(str, begin, end);
    } else if(str[begin] == '('){
        is_first = 1;
        op = str[begin+1];
        i = begin + 2;
        for(j = i + 1; j < end; j ++){
            while(str[i] == ' ') i ++;

            /* sub structure */
            if(str[i] == '('){
                p_count = 1;
                for(j = i+1; j <= end; j ++){
                    if(str[j] == ')') p_count --;
                    if(str[j] == '(') p_count ++;
                    if(p_count == 0) { j ++; break; }
                }
            } else {
                /* simple case */
                for(j = i+1; j <= end; j ++){
                    if(str[j] == ' ' || str[j] == ')') break;
                }
            }
            if(is_first){
                result = cal(str, i, j - 1);
                is_first = 0;
            } else {
                op_result(op, &result, cal(str, i, j - 1));
            }
            i = j + 1;
        }
    } else{
        error("invalid begin char");
    }
    return result;
}

int main(){
    char str[MAX_INPUT_SIZE];
    int result;

    fgets(str, MAX_INPUT_SIZE, stdin);
    /* remove the trailing \n */
    str[strlen(str) - 1] = 0;
    
    result = cal(str, 0, strlen(str) - 1);
    if(g_error){
        printf("Syntax Error.\n");
    } else {
        printf("%d\n", result);
    }
    return 0;
}