this is due to the buffer, when the user enters 1 char like A for example then presses enter, what is stored in the buffer is A\n, which are 2 characters. if the user enters 2 chars like A then K then press enter, what is stored in the buffer is AK\n, when you use scanf, it will read only the first char which is A then it will leave the other characters in the buffer. then you have to flush your buffer, you can use fflush(stdin); to do that but it's UB (undefined behavior and not portable) for most compilers, the other way to do that is to use the fgets method with a dummy char array, so instead of writing :
scanf("%c", &player1);
you can write
scanf("%c", &player1);
fgets(dummyBuffer, sizeof(dummyBuffer), stdin);
where dummyBuffer is a dummy char buffer defined at the beginning. and you can use it to clear your buffer.
and here is the full code with this only small modification:
#include <stdio.h>
int main(void){
char player1, player2;
char dummyBuffer[20];
do
{
printf("Enter Player 1 choice ('A','B','C') \n");
scanf("%c", &player1);
fgets(dummyBuffer, sizeof(dummyBuffer), stdin);
if(player1 != 'A' && player1 != 'B' && player1 != 'C')
{
printf("Invalid input! \n");
}
} while (player1 != 'A' && player1 != 'B' && player1 != 'C');
do
{
printf("Enter Player 2 choice ('A','B','C') \n");
scanf("%c", &player2);
fgets(dummyBuffer, sizeof(dummyBuffer), stdin);
if(player2 != 'A' && player2 != 'B' && player2 != 'C'){
printf("Invalid input! \n");
}
} while (player2 != 'A' && player2 != 'B' && player2 != 'C');
return 0;
}
and this is the output:
Enter Player 1 choice ('A','B','C')
D
Invalid input!
Enter Player 1 choice ('A','B','C')
A
Enter Player 2 choice ('A','B','C')
K
Invalid input!
Enter Player 2 choice ('A','B','C')
B
