Category: Embedded

C语言实现个位数的四则运算

Posted on by yuzifu

前提：
1，参与运算的数值为0－9的个位数
2，没有包含括号
3，输入的表达式是正确的
4，除法进行的是整除运算

代码：

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long calc(char *str)
{
    long fst,snd,trd,idx=0;
    char fop,nop;
 
    fst=str[0]-48;
    fop=str[++idx];
    snd=str[++idx]-48;
    do
    {
        nop=str[idx+1];
 
        if(fop=='+'||fop=='-')
        {
            if(nop=='+'||nop=='-'||nop=='\0')
            {
                switch(fop)
                {
                case '+':fst+=snd;break;
                case '-':fst-=snd;break;
                case '*':fst*=snd;break;
                case '/':fst/=snd;break;
                }
                if(nop=='\0')
                    break;
                fop=str[++idx];
                snd=str[++idx]-48;
            }
            else if(nop=='*'||nop=='/')
            {
                idx+=2;
                trd=str[idx]-48;
                snd=nop=='*'?snd*trd:snd/trd;
            }
        }
        else if(fop=='*'||fop=='/')
        {
            fst=fop=='*'?fst*snd:fst/snd;
            fop=str[++idx];
            snd=str[++idx]-48;
        }
        else
        {
            break;
        }
    }
    while(1);
 
    return fst;
}

演示：

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6+8-3*4/2=8
4*5/2-9+5=6
1+2-3-4+5=1
4*2*3*9*5=1080
4*2*3-9+5/2=17
4+2-3*9/7+5-2=6