i need help with my loop in C

[datainjector]

//The problem with my programm is when i try to come out of the loop by entering -1 it does not...Plz help me out guys i need help ....
// Puttsardara dey (KAZDAX)





#include <stdio.h>

int main()
{
int avg, gal, drive, cnt ,mg;
cnt = 1;

clrscr();

while ( gal != -1 ){
printf("\nEnter the gallons used ( -1 to end ): ");
scanf("%d", &gal);
printf("\nEnter the miles driven: ");
scanf("%d", &drive);
mg = drive/gal;
printf("\nThe miles / gallon for this tank was %d\n",mg);

cnt++;
}

if ( gal == -1 ) {
avg = mg/cnt;
printf("\nThe overall average miles/gallon for this tank was %d\n",avg);
}




getch();
return 0;
}

[quzah]

while ( gal != -1 ){
printf("\nEnter the gallons used ( -1 to end ): ");
scanf("%d", &gal);
printf("\nEnter the miles driven: ");
scanf("%d", &drive);
mg = drive/gal;
printf("\nThe miles / gallon for this tank was %d\n",mg);

cnt++;
}

if ( gal == -1 ) {
avg = mg/cnt;
printf("\nThe overall average miles/gallon for this tank was %d\n",avg);
}

You should change the order here. Try this:

do
{ 
    printf("\nEnter the gallons used ( -1 to end ): "); 
    scanf("%d", &gal); 

    if( gal != -1 ) 
    {
        printf("\nEnter the miles driven: "); 
        scanf("%d", &drive); 
        mg = drive/gal; 
        printf("\nThe miles / gallon for this tank was %d\n",mg); 
        cnt++; 
    }
}
while ( gal != -1 );

avg = mg/cnt; 
printf("\nThe overall average miles/gallon for this tank was %d\n",avg);

You may want to tweak your math a bit. (You may not need to, I'm tired and don't feel like compiling this or working it out in my head.) Anyway, that will fix your loop problem.

You could replace the do/while with a simple 'while' but you'd want to make sure and initialize 'gal' first before using it.

Quzah.

[vsriharsha]

Mmmm, I dont see any problem with ur code except that even after you enter -1, it will to calculate the miles/gallon and then exit the loop. The loop is getting exitted when the value of gal is -1...

[Nick]

Are you sure you want to use integer divison in calculating the avg?

Coding a while loop like

int c;
while(c != -1) { }

is very bad as there is a chance that
the uninitialized variable c could equal -1.