Question

And does each expression in the else if must test the same variable ? Please give example for the second question.
And can any expression be used for the IF expression ?
And in SWITCH statement, each case can have only one statement or more ? If we can put more than 1 statement, then what is the syntax for it ?

case 1:
      printf("Blah Blah");
      printf("Blah blah blah");

Or

case 1:
      {
      printf("Blah Blah");
      printf("Blah blah blah");
      }

Yes these are all silly question’s but I am still learning programming.
Thanks in advance.

Answer 1

if, else, “else if”

An if can have zero or one associated else clauses. Examples:

if (X)
    printf("if\n");

or

if (X)
    printf("if\n");
else
    printf("else\n");

These take only a single statement. If you want to use multiple statements (and some people say it’s better to do this even if you only have one statement per if/else), you have to use curly braces, like this:

if (X) {
    printf("if\n");
} else {
    printf("else\n");
}

You can also nest ifs:

if (X)
    printf("X\n");
else
    if (Y)
        printf("Y\n");
    else
        printf("something else\n");

This is usually written in a more readable way, though:

if (X)
    printf("X\n");
else if (Y)
    printf("Y\n");
else
    printf("something else\n");

You see, the else if is nothing special, it’s just another form of laying out a nested if.

Again, if you want more than one statement in there, you need to use curly braces:

if (X) {
    printf("X\n");
    printf("X2\n");
} else if (Y) {
    printf("Y\n");
    printf("Y2\n");
} else {
    printf("something else\n");
    printf("yet another print\n");
}

switch/case

As for switch statements, there you don’t need curly braces. Note however that “cases fall through” which means that in this example all four printfs are actually executed:

switch (1) {
  case 1:
    printf("I will be printed!\n");
    printf("Me too!\n");
  case 2:
    printf("And me also! (although I probably shouldn't)\n");
  case 3:
    printf("Me as well!\n");
}

If you don’t want this (which is usually the case), you have to use an explicit break after the code in each case:

switch (1) {
  case 1:
    printf("I will be printed!\n");
    printf("Me too!\n");
    break;
  case 2:
    printf("I won't :(\n");
    break;
  case 3:
    printf("D'oh!\n");
    break;
}

Blocks

By the way, the curly braces rule can be generalized: At every place where a single statement is allowed, you can also use something like { ... }, which is called a block. The advantage of using blocks is that you can

1. Use multiple statements where only one would be allowed otherwise (e.g. in an if)
2. Declare variables at the beginning of every block! Thus, you can do something like the following case 3: { int x = 3; printf("%d\n", x); }.