97679fd4c2
* Minor formatting change and added a note on == * Code blocks are now styled as C-language syntax. * Added a note about the difference of `==` and `=` in the context of condition statements. * change the second #6 to 7
286 lines
7.7 KiB
Markdown
286 lines
7.7 KiB
Markdown
---
|
|
title: Conditional Statements
|
|
---
|
|
# Conditional Statements in C
|
|
Conditional Statements are also known as Branching Statements. They are so called because the program chooses to follow one branch or another.
|
|
|
|
## 1. if statement
|
|
This is the most simple form of the conditional statements. It consists of a Boolean expression followed by one or more statements. If the Boolean expression evaluates to **true**, then the block of code inside the 'if' statement will be executed. If the Boolean expression evaluates to **false**, then the first set of code after the end of the 'if' statement (after the closing curly brace) will be executed.
|
|
|
|
C programming language **_assumes any non-zero and non-null values as true_** and if it is **_either zero or null, then it is assumed as false_** value.
|
|
|
|
#### Syntax
|
|
```C
|
|
if(boolean_expression)
|
|
{
|
|
//Block of Statements executed when boolean_expression is true
|
|
}
|
|
```
|
|
|
|
#### Example
|
|
```C
|
|
int a = 100;
|
|
if(a < 200)
|
|
{
|
|
printf("a is less than 200\n" );
|
|
}
|
|
```
|
|
|
|
#### Result
|
|
`a is less than 200`
|
|
|
|
## 2. if...else statement
|
|
If the Boolean expression evaluates to **true**, then the if block will be executed, otherwise, the else block will be executed.
|
|
|
|
#### Syntax
|
|
```C
|
|
if(boolean_expression)
|
|
{
|
|
//Block of Statements executed when boolean_expression is true
|
|
}
|
|
else
|
|
{
|
|
//Block of Statements executed when boolean_expression is false
|
|
}
|
|
```
|
|
|
|
#### Example
|
|
```C
|
|
int a = 300;
|
|
if(a < 200)
|
|
{
|
|
printf("a is less than 200\n");
|
|
}
|
|
else
|
|
{
|
|
printf("a is more than 200\n");
|
|
}
|
|
```
|
|
|
|
#### Result
|
|
`a is more than 200`
|
|
|
|
## 3. if...else if...else statement
|
|
When using if...else if..else statements, there are few points to keep in mind -
|
|
- An **if** can have **zero or one else**'s and it **must come after any else if**'s.
|
|
- An **if** can have **zero to many else if**'s and they **must come before the else**.
|
|
- Once an **else if** succeeds, none of the remaining else if's or else's will be tested.
|
|
|
|
#### Syntax
|
|
```C
|
|
if(boolean_expression_1)
|
|
{
|
|
//Block of Statements executed when boolean_expression_1 is true
|
|
}
|
|
else if(boolean_expression_2)
|
|
{
|
|
//Block of Statements executed when boolean_expression_1 is false and boolean_expression_2 is true
|
|
}
|
|
else if(boolean_expression_3)
|
|
{
|
|
//Block of Statements executed when both boolean_expression_1 and boolean_expression_2 are false and boolean_expression_3 is true
|
|
}
|
|
else
|
|
{
|
|
//Block of Statements executed when all boolean_expression_1, boolean_expression_2 and boolean_expression_3 are false
|
|
}
|
|
```
|
|
|
|
#### Example
|
|
```C
|
|
int a = 300;
|
|
if(a == 100)
|
|
{
|
|
printf("a is equal to 100\n");
|
|
}
|
|
else if(a == 200)
|
|
{
|
|
printf("a is equal to 200\n");
|
|
}
|
|
else if(a == 300)
|
|
{
|
|
printf("a is equal to 300\n");
|
|
}
|
|
else
|
|
{
|
|
printf("a is more than 300\n");
|
|
}
|
|
```
|
|
|
|
#### Result
|
|
`a is equal to 300`
|
|
|
|
## 4. Nested if statement
|
|
It is always legal in C programming to nest if-else statements, which means you can use one if or else if statement inside another if or else if statement(s).
|
|
|
|
#### Syntax
|
|
```C
|
|
if(boolean_expression_1)
|
|
{
|
|
//Executed when boolean_expression_1 is true
|
|
if(boolean_expression_2)
|
|
{
|
|
//Executed when both boolean_expression_1 and boolean_expression_2 are true
|
|
}
|
|
}
|
|
|
|
```
|
|
#### Example
|
|
```C
|
|
int a = 100;
|
|
int b = 200;
|
|
if(a == 100)
|
|
{
|
|
printf("a is equal to 100\n" );
|
|
if(b == 200)
|
|
{
|
|
printf("b is equal to 200\n");
|
|
}
|
|
}
|
|
|
|
```
|
|
#### Result
|
|
```bash
|
|
a is equal to 100
|
|
b is equal to 200
|
|
```
|
|
|
|
## 5. Switch Case Statement
|
|
The switch statement is often faster than nested if...else (not always). Also, the syntax of switch statement is cleaner and easy to understand.
|
|
|
|
### Syntax of switch case
|
|
```C
|
|
switch (n)
|
|
{
|
|
case constant1:
|
|
// code to be executed if n is equal to constant1;
|
|
break;
|
|
|
|
case constant2:
|
|
// code to be executed if n is equal to constant2;
|
|
break;
|
|
.
|
|
.
|
|
.
|
|
default:
|
|
// code to be executed if n doesn't match any constant
|
|
}
|
|
```
|
|
|
|
When a case constant is found that matches the switch expression, control of the program passes to the block of code associated with that case.
|
|
|
|
In the above pseudocode, suppose the value of n is equal to constant2. The compiler will execute the block of code associate with the case statement until the end of switch block, or until the break statement is encountered.
|
|
|
|
The break statement is used to prevent the code running into the next case.
|
|
|
|
### Example:
|
|
```C
|
|
// Program to create a simple calculator
|
|
// Performs addition, subtraction, multiplication or division depending the input from user
|
|
|
|
# include <stdio.h>
|
|
|
|
int main()
|
|
{
|
|
|
|
char operator;
|
|
double firstNumber,secondNumber;
|
|
|
|
printf("Enter an operator (+, -, *, /): ");
|
|
scanf("%c", &operator);
|
|
|
|
printf("Enter two operands: ");
|
|
scanf("%lf %lf",&firstNumber, &secondNumber);
|
|
|
|
switch(operator)
|
|
{
|
|
case '+':
|
|
printf("%.1lf + %.1lf = %.1lf",firstNumber, secondNumber, firstNumber+secondNumber);
|
|
break;
|
|
|
|
case '-':
|
|
printf("%.1lf - %.1lf = %.1lf",firstNumber, secondNumber, firstNumber-secondNumber);
|
|
break;
|
|
|
|
case '*':
|
|
printf("%.1lf * %.1lf = %.1lf",firstNumber, secondNumber, firstNumber*secondNumber);
|
|
break;
|
|
|
|
case '/':
|
|
printf("%.1lf / %.1lf = %.1lf",firstNumber, secondNumber, firstNumber/secondNumber);
|
|
break;
|
|
|
|
// operator is doesn't match any case constant (+, -, *, /)
|
|
default:
|
|
printf("Error! operator is not correct");
|
|
}
|
|
|
|
return 0;
|
|
}
|
|
```
|
|
|
|
### Output
|
|
```
|
|
Enter an operator (+, -, *,): -
|
|
Enter two operands: 32.5
|
|
12.4
|
|
32.5 - 12.4 = 20.1
|
|
```
|
|
The '-' operator entered by the user is stored in operator variable. And, two operands 32.5 and 12.4 are stored in variables firstNumber and secondNumber respectively.
|
|
|
|
Then, control of the program jumps to
|
|
```C
|
|
printf("%.1lf / %.1lf = %.1lf",firstNumber, secondNumber, firstNumber/firstNumber);
|
|
```
|
|
Finally, the break statement ends the switch statement.
|
|
|
|
If break statement is not used, all cases after the correct case is executed.
|
|
|
|
## 6. A note on equality `==`
|
|
|
|
When doing a comparison for the `if` statement, be very careful to use the equality operator `==` and not an assignment operator `=`. If an assignment operator `=` is used, the variable is overwritten and a `True` is returned. Consider the following code:
|
|
|
|
```C
|
|
#include <stdio.h>
|
|
|
|
int main(void) {
|
|
int x = 5;
|
|
if (x == 5) {
|
|
printf("1. x is %i\n",x);
|
|
}
|
|
|
|
if (x = 4) {
|
|
printf("2. x is %i\n",x);
|
|
}
|
|
}
|
|
```
|
|
### Output
|
|
```
|
|
1. x is 5
|
|
2. x is 4
|
|
```
|
|
As seen above, both `if` blocks are executed. In the second, the value of `x` is has been overwritten to `4`, which may not be what you want.
|
|
|
|
## 7. Ternary operation
|
|
The ternary operator (AKA conditional operator) is an operator that takes three arguments. The first argument is a comparison argument, the second is the result upon a true comparison , and the third is the result upon a flase comparison .It can be thought of as a shortened way of writing an if-else statement. It is often used to to assign variables based on the result of a comparison.
|
|
|
|
#### Syntax
|
|
```C
|
|
v = (conditional_statement) ? value_if_true : value_if_false
|
|
```
|
|
|
|
#### Example
|
|
```C
|
|
int a, b = 10, c = 100;
|
|
a = (b > c) ? 1 : 2;
|
|
printf("%d", a);
|
|
```
|
|
|
|
#### Result
|
|
`2`
|
|
|
|
### More Information
|
|
https://www.dotnettricks.com/learn/c/conditional-statements-if-else-switch-ladder
|
|
https://www.programiz.com/c-programming/c-if-else-statement
|
|
http://www.tutorialspoint.com/ansi_c/c_control_statements.htm
|