i have to use getchar(); twice to end program [duplicate] - c

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Closed 10 years ago.
Possible Duplicate:
Why doesn't getchar() wait for me to press enter?
I continue to learn C, and at this stage I have something that is not clear to me.
When I write a program, that has several printf();, at the end, where I ask a user to press Enter key to finish the program, I have to write getchar(); twice, because when I write it once it does not work. I use getchar(); only at the end of the program, nowhere else.
I work on Ubuntu. I write in C.
here is my latest work:
#include<stdio.h>
main()
{
int m,n,r,k,q,l;
printf("This program will help you to find GCD & LCM of 2 non-negative integers\n");
printf("Now, you'll be asked to enter your integers, press Enter to continue");
getchar();
printf("Enter first integer:");
scanf("%i", &m);
printf("Enter second integer:");
scanf("%i", &n);
while(m<0 || n<0)
{
printf("The integers cannot be negative! You'll be asked to enter integers again.\n");
printf("Enter first integer:");
scanf("%i", &m);
printf("Enter second integer:");
scanf("%i", &n);
}
while(m==0 && n==0)
{
printf("Both of the integers cannot be zero at the same time! You'll be asked to enter integers again.\n");
printf("Enter first integer:");
scanf("%i", &m);
printf("Enter second integer:");
scanf("%i", &n);
}
if(n>m)
{
int b;
b=n;
n=m;
m=b;
}
r=m%n;
if(r==0)
{
printf("The GCD of these integers is %i\n", n);
printf("The LCM of these integers is %i\n", m);
printf("Press Enter to finish");
getchar();
getchar();
return 0;
}
k=n%r;
while(k>0)
{
r=k;
k=q;
}
l=(m*n)/r;
printf("The GCD of these integers is %i\n", r);
printf("The LCM of these integers is %i\n", l);
printf("Press Enter to finish");
getchar();
getchar();
return 0;
}

Answer 1

The reason you need 2 getchar() is because
the last scanf() call left the ENTER waiting in the buffer
the 1st getchar() "ate" that ENTER
the 2nd getchar() waits for input.
To properly deal with user input, use fgets() and sscanf() instaed of the simpler scanf(). Define a buffer for these functions, for example
char buffer[1000];
and then replace your scanf() calls with the pair
fgets(buffer, sizeof buffer, stdin);
sscanf(buffer, "%d", &n);
In the future you might want to also check the return value of sscanf() to detect invalid inputs, like foo42ENTER
if (sscanf(buffer, "%d", &n) != 1) /* invalid input */;
Edit (using strtol() rather than sscanf() is even better -- thanks to #Scooter)
char buffer[1000];
char *err;
/* ... */
fgets(buffer, sizeof buffer, stdin); /* error checking ommited */
n = strtol(buffer, &err, 10);
/* error checking ommited */
/* ... */