Error Notes
C
01-scanf

C Error Notes

Problems with %c

scanf() only takes the characters it needs from the buffer, but this can cause issues when using %c. Consider the following program. When scanf() reads an integer, it leaves behind a newline character ('\n') in the input buffer. The next time scanf() is called with %c, it thinks this leftover '\n' is the input character. Because of this, the program never gets to read the tax status input from the buffer.

Buffer?
A buffer is like a temporary storage spot in a computer's memory. It holds data for a short time while it's being moved from one place to another.

#include <stdio.h>
 
int main(void)
{
    int items;
    char status; // tax status g or p
 
    printf("Number of items : ");
    scanf("%d", &items);
 
    printf("Status : ");
    scanf("%c", &status);   // ERROR: assigns \n to variable 'status'
                            //        and will not pause for user input
 
    printf("%d items (%c)\n", items, status);
 
    return 0;
}

The above program produces the following output:

Number of items : 25
Status : 25 items (
)

Notice how the newline character ('\n') (which was assigned to the tax status variable) places the closing parenthesis on a newline.

Method-1:

scanf("%d", &items);
scanf("%c%c", &junk, &status); // store one character in junk first

Method-2:

scanf("%d", &items);
scanf("%*c%c", &status);       // discard(ignore) one character first

Method-3:

scanf("%d", &items);
scanf(" %c", &status);         // discard(ignore) all whitespace first

Method-4:

scanf("%d%*c", &items);        // discard(ignore) newline ('\n')
scanf("%c", &status);

Method-5:

scanf("%d", &items);
clear();                       // call a custom function to clear the buffer
scanf("%c", &status);
1768. Merge Strings Alternately01-Wsign-compare