The program doesn't stop on scanf(“%c”, &ch) line, why? [duplicate]

Answer 1

The reason behind this is the newline \n character left behind by previous scanf, when pressing Enter key, for the next read of scanf. When the statement

scanf("%c", &ch);   

executed then it reads that \n left behind by the previous scanf.
To eat up this \n you can use a space before %c specifier. A space before the %c specifier is able to eat up any number of white-space characters.

scanf(" %c", &ch);   
       ^ a space

Answer 2

Let's say you input 2 when you're reading for num. The actual input stream will be 2\n (\n is the newline character). 2 goes into the num, and there remains \n, which goes into ch. To avoid this, add a whitespace in format specifier.

scanf(" %c", &ch); 

This will ignore any whitespaces, newlines or tabs.