字符串轉爲整數計算

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

int main(){
    char sign = '+';
    char addnum1[] = "1";
    char addnum2[] = "2";
    int res = 0;
    switch(sign)
    {
        case '+':
            res = atoi(addnum1) + atoi(addnum2);
            break;
        case '-':
            res = atoi(addnum1) - atoi(addnum2);
            break;;
        case '*':
            res = atoi(addnum1) * atoi(addnum2);
            break;
        case '/':
            if(atoi(addnum2) == 0)
            {
                res = -1;
                break;
            }

            res = atoi(addnum1) / atoi(addnum2);
            break;

        default:
            res = -1;
            break;
    }

    printf("result:%d\n",res);
    return 0;
}
                           

#include<stdio.h>
#include <stdlib.h>
int main(){
    char addnum1[] = "1";
    char addnum2[] = "2";
    int num1 = 0;
    int num2 = 0;
    int res = 0;
    num1 = atoi(addnum1);
    num2 = atoi(addnum2);
    res = num1 + num2;
    printf("result = %d\n",res);
    return 0;
}