Question

I wrote a program that accepts a character of input and outputs that character, like this

int ch = getchar();
printf("%c", ch);

It worked like I expected. Then I decided to be welcoming and print Hello first.

printf("Hello!\n");
int ch = getchar();
printf("%c", ch);

To my surprise, this caused the compiler to throw two errors:

error C2065: ‘ch’ : undeclared identifier
error C2143: syntax error : missing ‘;’ before ‘type’

I didn’t see why adding the first line would cause that to happen. Anyway, I refactored the program to get rid of the int declaration and the errors magically disappeared.

printf("Hello!\n");
printf("%c", getchar());

What’s going on? What’s the magic that causes these errors to appear and then disappear?

Answer 1

Creating new variables after the start of a block was not allowed in C89 standard but is allowed in the newer C99 standard.

You are using a older compiler or a compiler not fully compliant to c99.
Your code example should work as is on any good compiler. Works on gcc-4.3.4

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Alternate Solutions:

You can get rid of the problems in two ways:
Declare the variable at the begining of the block:

int ch;
printf("Hello!\n");
ch = getchar();
printf("%c", ch);

Or

Create a new block for declaring the variable:

printf("Hello!\n");
{ 
    int ch = getchar();
    printf("%c", ch);
}

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Suggestion:

You should really change your compiler because if i remember correctly gcc supported this as compiler extension even prior to c99.