Not asking for char "choose" Before switch statement [closed] - c

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This code executes itself without asking for char "choose" for further processing before the switch statement scanf("%c",&choose); switch(choose).
printf("enter option 1,2,3 or 4 \n\n");
scanf("%c",&choose); // why it not ask to input char
switch(choose)
{
case '1': case '+':
{
printf("enter 1st value\n");
scanf("%f",&a);
printf("enter 2st value\n");
scanf("%f",&b);
c=a+b;
printf("%f + %f = %f",a,b,c);
break;
}
case '2': case '-':
{
printf("enter 1st value\n");
scanf("%f",&a);
printf("enter 2nd value\n");
scanf("%f",&b);
c=a-b;
printf("%f - %f = %f",a,b,c);
break;
}
case '3': case'*':
{
printf("enter 1st value\n");
scanf("%f",&a);
printf("enter 2nd value\n");
scanf("%f",&b);
c=a*b;
printf("%f * %f = %f",a,b,c);
break;
}
}

Answer 1

printf("enter option 1,2,3 or 4 \n\n");
scanf("%c",&choose);
In your code if you are using any scanf before the above given code, then this behaviour is expected as the previous scanf reads the input leaving \n in the input buffer which is feeded as input to next scanf.
To overcome this issue please use fflush(stream) before scanf(...), this should solve the problem.
fflush(stdin);
or you can use getchar() function, this will alse solve your the issue.

Answer 2

Probably because you've already input something earlier, so that there are non-scanned characters left in the buffer which this "greedy" scanf() then scans without stopping.
You should check the return value of scanf() to learn if it succeeded or not.
And you should switch to using fgets() to read in a whole line, and then parse that. It's much safer and easier to predict, that way.

Answer 3

I've executed it without any problems (it gets the "choose" char):
#include <stdio.h>
int main(int argc, char *argv ) {
char choose;
float a,b,c;
printf("enter option 1,2,3 or 4 \n\n");
scanf("%c",&choose); // why it not ask to input char
switch(choose)
{
case '1': case '+':
{
printf("enter 1st value\n");
scanf("%f",&a);
printf("enter 2st value\n");
scanf("%f",&b);
c=a+b;
printf("%f + %f = %f",a,b,c);
break;
}
case '2': case '-':
{
printf("enter 1st value\n");
scanf("%f",&a);
printf("enter 2nd value\n");
scanf("%f",&b);
c=a-b;
printf("%f - %f = %f",a,b,c);
break;
}
case '3': case'*':
{
printf("enter 1st value\n");
scanf("%f",&a);
printf("enter 2nd value\n");
scanf("%f",&b);
c=a*b;
printf("%f * %f = %f",a,b,c);
break;
}
}
return 0;
}
Probably its something you didn't read before...
I'm guessing that you are doing a similar "scanf("%c",&choose);" before, so the next read you will get the carriage return.
You could try to change the following lines:
scanf("%c",&choose);
for:
scanf("%c%*c",&choose);
...so you discard the \n
If this don't solve your issue, maybe you should provide more code :)