我想编的程序是这样的：

Enter the gallons used(-1 to end):12.8

Enter the miles driven:287

The miles/gallon for this tank was 22.421875

 

Enter the gallons used(-1 to  end):10.3

Enter the miles driven:200

The miles /gallon for this tank was 19.417475

 

Enter the gallons used(-1 to end):5

Enter the miles driven :120

The miles/gallon for this tank was 24.000000

 

Enter the  galons used (-1 to end ): -1

The overall average miles /gallon was 21.601423

 

 

 

 

我所编的程序如下：

#include<stdio.h>
main()
{
float gallons,miles,result,average,counter,total;
 counter=0;
 total=0;
 while(gallons!=-1){
 printf("\nEnter the gallons used(-1 to end):");
 scanf("%f",&gallons);
 printf("\nEnter the miles driven:");
 scanf("%f",&miles);
 result=miles/gallons;
 counter=counter+1;
 printf("The miles/gallon for this tank was%f\n",result);}
 if(gallons=-1){
total=result+result;
average=(float)total/counter;
printf("\nThe overal average miles/gallon was%f",average);}
 }

请问这里有什么错误，我非常渴望知道自己的错误，因为我还是菜鸟。

当你第一次输入12.8和287的时候,程序输出22.42没错,第二次和第三次也没错,
第四步,当你输入-1的时候,程序就全部执行一次,问题出现了.

应该是这样：#include<stdio.h>
main()
{
float gallons,miles,result,average,counter,total;
counter=0;
total=0;
miles=0;
gallons=0;
average=0;result=0;
printf("\nEnter the gallons used(-1 to end):");
scanf("%f",&gallons);
while(gallons>=0){
printf("Enter the miles driven:");
scanf("%f",&miles);
result=miles/gallons;
counter=counter+1;
total=total+result;
average=(float)total/counter;

printf("The miles/gallon for this tank was%f\n",result);
printf("\nEnter the gallons used(-1 to end):");
scanf("%f",&gallons);
}
if(gallons<0){
printf("\nThe overal average miles/gallon was%f\n",average);}
}



又或者是这样：#include<stdio.h>
int main()
{
float gallons,miles ,total,average,counter,Z;
      gallons=0;
      miles=0;
      total=0;
      average=0;
      counter=0;
      Z=0;
      while(gallons>=0){
         printf("\nEnter the gallons used(-1 to end):");
         scanf("%f",&gallons);
         if(gallons<0){
         printf("\nThe overall average miles/gallon was%f\n",average);
         return 0;}
         printf("Enter the miles driven:");
         scanf("%f",&miles);
         Z=miles/gallons;
         counter=counter+1;
         total=Z+total;
         average=total/counter;
         printf("The miles/gallon for this tank was%f\n",Z);}
         printf("\nThe overall average miles/gallon was%f\n",average);
         return 0;
}


总之都要感谢你们的帮忙