prog.c: In function ‘main’:
prog.c:10:3: error: duplicate case value
case 'c':
^~~~
prog.c:8:3: note: previously used here
case 'c':
^~~~
prog.c:6:2: warning: ignoring return value of ‘scanf’, declared with attribute warn_unused_result [-Wunused-result]
scanf("%c", &c);
^~~~~~~~~~~~~~~