实现 ./hello 35 - 5 ---->30 ./hello 35 + 5 ----> 40 ./hello 35 / 5 ----> 7 ./hello 5 \* 7 ----> 35

#include <stdio.h>
int main(int argc, char *argv[])
{
    int a, b;
    char c;
    if(argc < 4)
    {
        printf("param error like this: ./a.out 35 - 5\n");
        return 0;
    }
    a = atoi(argv[1]);
    b = atoi(argv[3]);
    c = *argv[2];        //argv[2] (char *)---> "+"     char *p = "+";       *p = '+';
    switch(c)
    {
    case '+':
        printf("%d\n", a + b);   break;
    case '-':
        printf("%d\n", a - b);   break;
    case '*':
        printf("%d\n", a * b);   break;
    case '/':
        printf("%d\n", a / b);   break;
    }
}