#include <stdio.h>
main()
{float x,u[5],v[5],sum;
int i;
x[5]={0.4,0.55,0.8,0.9,1};
y[5]={0.41075,0.57815,0.88811,1.02652,1.17520};
scanf("%f",&x);
u[0]=0.41075*(x-x[1])*(x-x[2])*(x-x[3])*(x-x[4])；
u[1]=0.57815*(x-x[0])*(x-x[2])*(x-x[3])*(x-x[4]);
u[2]=0.88811*(x-x[0])*(x-x[1])*(x-x[3])*(x-x[4]);
u[3]=1.02652*(x-x[0])*(x-x[1])*(x-x[2])*(x-x[4]);
u[4]=1017520*(x-x[0])*(x-x[1])*(x-x[2])*(x-x[3]);
v[0]=(0.4-0.55)*(0.4-0.8)*(0.4-0.9)*(0.4-1.0);
v[1]=(0.55-0.4)*(0.55-0.8)*(0.55-0.9)*(0.55-1);
v[2]=(0.8-0.4)*(0.8-0.55)*(0.8-0.9)*(0.8-1.0);
v[3]=(0.9-0.4)*(0.9-0.55)*(0.9-0.8)*(0.9-1.0);
v[4]=(1.0-0.4)*(1.0-0.55)*(1.0-0.8)*(1.0-0.9);
for(i=0;i<=4;i++)sum=sum+u[i]*v[i];
printf("%f",sum);
}

因为你语法错了呀  很简答啊

float x,u[5],v[5],sum;
int i;
x[5]={0.4,0.55,0.8,0.9,1};
y[5]={0.41075,0.57815,0.88811,1.02652,1.17520};

x 你定义了什么，y定义了吗？

两个数组都没定义就使用了，是该出错提示下了

x[5]={0.4,0.55,0.8,0.9,1};
y[5]={0.41075,0.57815,0.88811,1.02652,1.17520};
这两行的数组没有被定义，应该在数组之前加一个float ,并且x数组和变量x会冲突
u[0]=0.41075*(x-x[1])*(x-x[2])*(x-x[3])*(x-x[4])；
这一行的最后一个分号不能在汉语输入状态下输入，编译时会无法识别。
小菜鸟，只看到这两个问题。