If conditions & switch

if true, do A, otherwise, do B

Selection Statements

Selection statements modify the control flow of the program. It uses different sets of code depending on the condition at runtime.

If Statements

Code blocks are bounded by a set of {}, which you have already seen, surrounds the main() function.

The if statements take the following formats:

• if (<expression>) <statement_true>

• if (<expression>) <statement_true> else <statement_false>

If expression evaluates to a non-zero value, then statement_true is evaluated. Otherwise, statement_false is evaluated if provided along with the else clause.

Often, statement_false is itself another if statement, chaining into an (if, else if, else) structure.

The following is an example:

uint32_t money = 100;
if (money) {
    printf("I have $%d.\n", money);
} else {
    printf("I have no money.\n");
}

//Console Output: I have $100.

money = money - 100;

if (money) {
    printf("I have $%d.\n", money);
}

//Console Output: (Literally nothing)

At the beginning, the value of money is 100. When the program is executing the first if statement, money is a non-zero value, so printf("I have $%d.\n", money); is executed.

The value of money is then substracted by 100, so the value is now equal to 0. Then when the program runs the second if statement, the if-block is skipped.

We can chain multiple if-conditions by writing another if-statement after an else.

The following is an example:

if (x > 85) {
    // if x > 85 evaluates to true, this part is run.
    // otherwise, this part is skipped.
} else if (x == 0) {
    // some other code
    // only runs if (x > 85) is false and if (x == 0) is true
} else {
    // some other code
    // only runs if both (x > 85) and (x == 0) are false
}

Switch Statements

Switch statements allow a variable to be tested for each case. It contains jump statements and labels, which we do not recommend using outside of switch statements. They act simply as alternatives to if statements on the superficial level. The format is as follows:

• switch (<expression>) <statement>

  The "expression" here must evaluate to some integral value. The "statement" here is typically a block with case labels.

• case <integer_constant_expression>: <statement>

• default: <statement>

switch (x) {//value to compare against with the cases
    case 1:
        //code for when x == 1
        break; //jumps the the end of the switch statement
    case 2:
        //code for when x == 2
    case 3:
        //code carries on from line above and for when x == 3
        break;
    default:
        //code when none of the cases match. The default label is optional
}

Each case is compared against the expression in the switch parenthesis, if a match is found, the program jumps to that case and starts executing line by line, and only exits when encountering break; or when the code block ends.

Basically, switch-statements are just if-statements when all their conditions are x == case.