#include<stdio.h>
#include<math.h>
#include<stdlib.h>
void main()
{
    FILE *rf,*wf;
    float a,b,c,d,e,f,g;
   
    if((rf=fopen("data1.txt","r"))==NULL){printf("cannot open file1\n");exit(0);}
     if((wf=fopen("result1.txt","w"))==NULL){printf("cannot open file2\n");exit(0);}

            

          while(!feof(rf))
          {
              fscanf(rf,"%d%d",&a,&b);
              {
                  f=a+b;
                   g=b-a;
                  c=sin(f);
                  d=log(b);
                  e=exp(g);
                  fprintf(wf,"a=%.2f\t b=%f\t c=%.2f\t d=%.2f\t e=%.2f\t ",a,b,c,d,e);
                  fprintf(wf,"\n\n");
              }
              fclose(rf);fclose(wf);
          }
}

fscanf(rf,"%f%f",&a,&b);

呵呵 失误啊 但是系统提示cannot open file1 为什么？

工程目录下面看看有没data1.txt，或者是不是后缀名有误。

对的。把 data1.txt 放到编译后生成的 exe 所在的文件夹即可

LZ，你每次写文件都要先关闭一下，不会让文件内部指针重置么？