C语言分段函数y=f(x)可表示为：2x+1(x<0)y=0(x=0)2x-1(x>0)编程实现输入一个x值，输出函数对应的y值。

#include <stdio.h>
double fun(double x)
{
    double y;
    if(x<0)
        y = 2*x+1;
    else if(x==0)
        y = 0;
    else
        y = 2*x-1;
    return x;
}
int main()
{
    double x,y;
    scanf("%lf",&x);
    y = fun(x);
    printf("%lf",y);
    return 0;
}

//2x+1(x<0)y=0(x=0)2x-1(x>0)
#include <stdio.h>
int main()
{
    float x,y;
    scanf("%f",&x);
    if(x<0)
        y = 2*x+1;
    else if(x==0)
       y = 0;
    else
       y = 2*x-1;
    printf("%f",y);
    return 0;
}