You are happily ignoring the
C
programming language rules, for instance that function
name
in the declaration
must match the one in the definition. Try:
#include<stdio.h>
float average_mileage(float start_mileage,float end_mileage);
int main()
{ float start_mileage,end_mileage,avg;
printf("Enter the starting mileage\n");
scanf("%f",&start_mileage);
printf("Enter Ending Mileage\n");
scanf("%f",&end_mileage);
avg=average_mileage(start_mileage,end_mileage);
printf("The average mileage is %f\n", avg);
return 0;
}
float average_mileage(float start_mileage,float end_mileage)
{float dt;
float total=1000;
float avg;
dt=start_mileage-end_mileage;
avg=dt/total;
return avg;
}