c - 递归函数？

功能

有人可以解释一下此代码的确切作用。这对我来说是一项任务，但我不太了解。

我尝试过这个。当我输入一个介于0到9之间的值时，它是否返回相同的值？

double fnord(double v){
    int c = getchar();
    if(c>='0' && c<='9')
        return fnord(v*10+(c-'0'));
    ungetc(c,stdin);
    return v;
}

在主要功能中，我这样做了：

int main(){
    double v;
    scanf("%lf",&v);
    printf("%lf",fnord(v));
}

最佳答案

#include <stdio.h>

// convert typed characters to the double number
// stop calculations if non digit character is encounter
// Example: input = 123X<enter>
// the first argument for fnord for  will have a value
// 0*10 + 1  (since '1' = 0x31 and '0' = 0x30)
// then recursive function is called with argument 1
// v= 1
// and digit '2' is entered
// v = 1*10 + 2 ((since '2' = 0x32 and '0' = 0x30)
// v= 12 and fnord will process third character '3' = 0x33
// v = 12*10 +3
// when 'X' is encountered in the input the processing will stop, (X is returned back to the input string)
// and when ENTER is ecountered the last calculated v is returned
// v = 123 as the double number.

double fnord(double v){
    int c = getchar();
    if(c>='0' && c<='9')
        return fnord(v*10+(c-'0'));
    ungetc(c,stdin);
    return v;
}

int main()
{
    double v=0;
    printf("%f",fnord(v));
    return 0;
}

输入：

    123X

输出：

    123.000000