一个简单的计算C语言四则运算

#include<stdio.h>
#include<string.h>
int main(void)
{
    char string[100];
    int index = 1;
    int sum = 0;
    int temval = 1;
    char ope, c,inope;
    memset(string, 0, 100);
    scanf("%s",string);

    sum += (string[0] - 48);
    while(string[index] != '\0')
    {
        c = string[index];
        switch(c)
        {
        case '+':ope = '+';index++;
            break;
        case '-':ope = '-';index++;
            break;
        case '*':ope = '*';index++;
            break;
        case '/':ope = '/';index++;
            break;
        default:temval = c - 48;index++;
            while(string[index] != '+'&&string[index] != '-'&&string[index] != '\0')
            {
                inope = string[index];
                if(inope == '*')
                {
                    temval *= (string[++index] - 48);
                    index++;
                }
                if(inope == '/')
                {
                    temval /= (string[++index] - 48);
                    index++;
                }
            }
            if(ope =='+')
            {
                
                sum +=temval;
            }
            if(ope == '-')
            {
                sum -= temval;
            }
        }
    }
    printf("\n表达式%s的值为:%d\n",string,sum);
    return 0;
}

 

计算类似1+2-3*3/3的表达式,如果输入的格式不正确，因为没有加入判断表达式是否正确，会出错的。