小白写了个代码，望大大给个指导。

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


int a, b, c;//定义三个整数变量


void main()
{
    printf("*****************************************************");
    printf("\n");
    printf("简单加减乘除计算器");
    printf("\n");
    printf("*****************************************************");
        printf("\n请输入第一个值：");
        scanf_s("%d", &a);
        //给a初始化赋值
        printf("\n请输入(1)+、(2)-、(3)*、(4)/括号内代表计算的数字：");
        scanf_s("%d", &b);
        //给b初始化赋值
        printf("\n请输入第二个值：");
        scanf_s("%d", &c);
        //给c初始化赋值
        if (b == 1)
        {
            printf("\n计算结果为%d\n", a + c);
            system("pause");
        }
        else if (b == 2)
        {
            printf("\n计算结果为%d\n", a - c);
            system("pause");
        }
        else if (b == 3)
        {
            printf("\n计算结果为%d\n", a * c);
            system("pause");
        }
        else if (b == 4)
        {
            printf("\n计算结果为%d\n", a / c);
            system("pause");
        }

}