Overview
A summary of branch statements in Objective-C.
Note
This post is based on Objective-C 2.0.
Introduction
The Branch Statements supported by Objective-C are as follows:
If Statement,Switch Statement
For decision-making using operators, please refer to the ternary operator section in the following post:
Summary
1. If Statement
If you have studied C, the If Statement should be familiar. It can be used in the following form:
if (<#condition#>) {
<#statements#>
}
if (<#condition#>) {
<#statements#>
} else if (<#expression#>) {
<#statements#>
} else {
<#statements#>
}
1.1. condition
A condition check is performed based on the given condition to determine whether to execute the statements logic within the conditional statement. If the condition is not satisfied, the execution flow moves downward.
Let us run a simple example:
int number = 0;
NSLog(@"Enter a positive multiple of 10.");
scanf("%d", &number);
int remainder = number % 10;
if (number > 0 && remainder == 0) {
NSLog(@"%d is a positive multiple of 10.", number);
} else {
NSLog(@"%d is not a positive multiple of 10.", number);
}
200
200 is a positive multiple of 10.
Program ended with exit code: 0
When the condition check logic is complex, splitting the conditions into logical units before reaching the if statement, as shown below, can improve compilation performance and readability.
int number = 0;
NSLog(@"Enter a positive multiple of 10.");
scanf("%d", &number);
BOOL isNumberGreaterThanZero = number > 0;
int remainder = number % 10;
BOOL isRemainderEqualToZero = remainder == 0;
BOOL isMultiplesOfTen = isNumberGreaterThanZero && isRemainderEqualToZero;
if (isMultiplesOfTen) {
NSLog(@"%d is a positive multiple of 10.", number);
} else {
NSLog(@"%d is not a positive multiple of 10.", number);
}
35
35 is not a positive multiple of 10.
Program ended with exit code: 0
However, when the condition involves comparison or logical operators and you pre-compute all operations, you may lose the benefit of Short Circuit Evaluation, so write appropriately depending on the situation.
For example, if you do not split the conditions beforehand:
if (number > 0 && (number % 10) == 0) {
...
}
When checking the first condition, if number is less than or equal to 0, the (number % 10) == 0 condition after && will not be checked and the if statement will be exited immediately.
However, if you split the conditions into logical units and perform the operations first, both conditions are always checked, resulting in slightly more unnecessary computation cost:
BOOL isNumberGreaterThanZero = number > 0;
int remainder = number % 10;
BOOL isRemainderEqualToZero = remainder == 0;
BOOL isMultiplesOfTen = isNumberGreaterThanZero && isRemainderEqualToZero;
if (isMultiplesOfTen) {
...
}
If you want to add more branch paths, you can use if-else constructs to add as many as needed:
int number = 0;
NSLog(@"Enter a positive multiple of 10.");
scanf("%d", &number);
BOOL isNumberGreaterThanZero = number > 0;
int remainder = number % 10;
BOOL isRemainderEqualToZero = remainder == 0;
if (isNumberGreaterThanZero == NO) {
NSLog(@"I said to enter a positive multiple of 10.");
} else if (isRemainderEqualToZero == NO) {
NSLog(@"%d is not a multiple of 10.", number);
} else {
NSLog(@"%d is a positive multiple of 10.", number);
}
In addition to simply adding paths, as shown in the above example, you can perform condition checks on single logical units, eliminating condition cases one by one to more clearly express the path to the final goal.
2. Switch Statement
The Switch Statement should also be familiar if you have studied C. It can be used in the following form:
switch (<#expression#>) {
case <#constant#>:
<#statements#>
break;
default:
break;
}
2.1. expression
A variable, constant, or expression that will be compared with the constant of each case.
2.2. constant
If the value of the case matches the value of the expression, the statements logic is executed. You must place break at the end of the case to execute only that case’s statements logic and exit the switch statement.
If you forget it, the statements logic of the case immediately below will also be executed. However, there are cases where break is intentionally omitted for implementing certain logic, and in such cases, the intent should be clearly indicated.
2.3. default
This case is executed when none of the cases match. Since there are no more cases below, break can be omitted, but make it a habit to add break at the end of every case. Otherwise, you will accidentally forget it.
Let us run a simple example:
char operator = '*';
switch(operator) {
case '+':
NSLog(@"Addition" );
break;
case '-':
NSLog(@"Subtraction" );
break;
case '*':
NSLog(@"Multiplication" );
break;
case '/':
NSLog(@"Division" );
break;
default:
NSLog(@"Not a valid operator" );
break;
}
Multiplication
Program ended with exit code: 0
Let us remove the break from the * case:
char operator = '*';
switch(operator) {
case '+':
NSLog(@"Addition" );
break;
case '-':
NSLog(@"Subtraction" );
break;
case '*':
NSLog(@"Multiplication" );
case '/':
NSLog(@"Division" );
break;
default:
NSLog(@"Not a valid operator" );
break;
}
Multiplication
Division
Program ended with exit code: 0
An unintended incorrect result occurred. The logic of the / case below the * case was also executed. Always watch out for unintended break omissions.
You can also intentionally omit break to have multiple cases execute a common piece of logic, like the following:
char operator = '*';
switch(operator) {
case '+':
NSLog(@"Addition" );
break;
case '-':
NSLog(@"Subtraction" );
break;
case '*':
case 'x':
NSLog(@"Multiplication" );
break;
case '/':
NSLog(@"Division" );
break;
default:
NSLog(@"Not a valid operator" );
break;
}
Multiplication
Program ended with exit code: 0
In such cases, as mentioned above, make sure the code itself clearly expresses the intent, or if that is not possible, write good comments.
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