Decision Structure in C, Boolean Operator and
Expression
In C programming, decision structures allow
you to make decisions in your code based on certain conditions. This is
typically achieved using `if`, `else if`, and `else` statements along with
Boolean operators and expressions. Boolean operators are used to compare values
and produce a result of either true (1) or false (0). Let's explore these
concepts with examples and their expected outputs.
1.
The goto Statement: In C programming, the `goto` statement is a control
statement that allows you to transfer the program's control to a labeled
statement within the same function or block of code. While `goto` can be a
powerful tool in some situations, it is generally discouraged and considered
bad practice because it can make code harder to understand and maintain.
Structured programming constructs like loops (`for`, `while`, `do-while`) and
conditional statements (`if`, `else`, `switch`) are preferred in most cases
because they provide clearer program flow and maintainability.
The basic syntax of the `goto` statement in
C is as follows:
goto label;
// ...
label:
// Statement(s) to execute
Here's a simple
example of how the `goto` statement can be used:
Example
#include <stdio.h>
int main() {
int i = 0;
start:
if
(i < 5) {
printf("%d ", i);
i++;
goto start; // Jump back to the 'start' label
}
return 0;
}
In this example, the program uses a `goto`
statement to create a loop. It repeatedly prints the value of `i` and
increments it until `i` is no longer less than 5. When `i` becomes 5, the
program exits the loop.
While this code works, it is generally not
recommended to use `goto` for creating loops or controlling program flow
because it can lead to "spaghetti code" that is difficult to read and
maintain. Instead, you should use structured control flow constructs like
`for`, `while`, and `do-while` loops to achieve the same results in a more
organized and understandable way,
Here's an example
of the same behaviour using a `while` loop, which is a better practice:
Example
#include <stdio.h>
int main() {
int i = 0;
while (i < 5) {
printf("%d ", i);
i++;
}
return 0;
}
In this `while` loop example, the code is more readable and
follows a structured approach to looping, making it easier to understand and
maintain.
2.
If Statement: The `if` statement is a fundamental control structure in
most programming languages, including C. It allows you to conditionally execute
a block of code based on the evaluation of a specified condition. The syntax of
the `if` statement in C is as follows:
if (condition) {
// Code to execute if the condition is true
}
Here's a breakdown of how the `if` statement works:
i. `if`: This keyword begins the `if` statement and
is followed by a set of parentheses `( )`. The condition you want to evaluate
goes inside these parentheses.
ii. `condition`: The condition is a boolean
expression that can be either true or false. It's the criteria you want to
test. If the condition evaluates to true, the code inside the block will be
executed. If it evaluates to false, the code inside the block will be skipped.
iii. `{ }` Block: The block of code enclosed within
curly braces `{ }` is the code that will be executed if the condition inside
the parentheses is true. This block can contain one or more statements, and it
is often indented for readability.
Here's an example
of how the `if` statement is used in C:
#include <stdio.h>
int main() {
int num = 10;
if
(num > 5) {
printf("The
number is greater than 5.\n");
}
printf("This
code always runs.\n");
return
0;
}
In this example, the condition `num >
5` is true because the value of `num` is 10, which is indeed greater than 5.
Therefore, the code inside the `if` block is executed, and "The number is
greater than 5." is printed. The code outside the `if` block, after the
`if` statement, is also executed regardless of the condition's outcome.
It's important to note that you can use
`if` statements in conjunction with `else` and `else if` statements to create
more complex branching logic, allowing your program to take different paths
based on different conditions. 2. If-Else Statement:
3.
`if-else` statement : The `if-else` statement is an extension of the basic `if`
statement in C programming. It allows you to create a decision-making structure
where you can specify two different blocks of code to be executed based on the
evaluation of a condition. If the condition is true, one block of code is
executed, and if it is false, another block of code is executed.
The syntax of the `if-else` statement is as follows:
if (condition) {
// Code to execute
if the condition is true
} else {
// Code to execute
if the condition is false
}
Here's a breakdown of how the `if-else` statement works:
1. `if`: This keyword starts the `if-else` statement
and is followed by a set of parentheses `( )`. Inside these parentheses, you
specify the condition you want to evaluate.
2. `condition`: The condition is a boolean expression
that can be either true or false. It's the criteria you want to test.
3. `{ }` Block (if true): The block of code enclosed within
curly braces `{ }` immediately after the `if` statement is the code that will
be executed if the condition is true.
4. `else`: After the closing curly brace `}`, the `else`
keyword is used to specify a block of code that will be executed if the
condition is false.
5. `{ }` Block (if false): The block of code enclosed within
curly braces `{ }` immediately after the `else` statement is the code that will
be executed if the condition is false.
Here's an example of how the `if-else`
statement is used in C:
#include <stdio.h>
int main() {
int num = 3;
if (num > 5) {
printf("The
number is greater than 5.\n");
}
else {
printf("The
number is not greater than 5.\n");
}
printf("This
code always runs.\n");
return 0;
}
In this example, the condition `num > 5`
is false because the value of `num` is 3, which is not greater than 5.
Therefore, the code inside the `else` block is executed, and "The number
is not greater than 5." is printed. The code outside the `if-else` block,
after the `if-else` statement, is also executed regardless of the condition's
outcome.
The `if-else` statement is crucial for
creating branching logic in your programs, allowing you to handle different
cases or outcomes based on the evaluation of a condition. You can also chain
multiple `if-else` statements together to create more complex decision
structures.
The `if-else` statement allows you to
execute one block of code if a condition is true and another block if it's
false.
#include <stdio.h>
int main() {
int x = 3;
if (x > 5) {
printf("x
is greater than 5.\n");
}
else {
printf("x
is not greater than 5.\n");
}
return 0;
}
Output:
x is not greater than 5.
4. If-Else If-Else
Statement:
In C programming, an
"if-else if-else" statement is used to create a conditional branching
structure that allows you to execute different blocks of code based on multiple
conditions. It provides a way to handle multiple possible outcomes in a
program.
The basic syntax of an "if-else
if-else" statement in C is as follows:
if (condition1) {
//
Code to execute if condition1 is true
} else if (condition2)
{
//
Code to execute if condition1 is false and condition2 is true
} else
{
//
Code to execute if both condition1 and condition2 are false
}
Here's how the "if-else if-else" statement
works:
1. The program evaluates the condition1. If condition1 is
true, the code block inside the first `if` statement is executed, and then the
program exits the entire `if-else if-else` structure.
2. If condition1 is false, the program evaluates condition2.
If condition2 is true, the code block inside the `else if` statement is
executed, and then the program exits the structure.
3. If both condition1 and condition2 are false, the code
block inside the `else` statement is executed.
You can have multiple `else if` blocks to
test additional conditions. The first condition that evaluates to true will
execute its corresponding block of code, and the program will exit the entire
structure.
Here's an example of how you might use an
"if-else if-else" statement in C:
#include <stdio.h>
int main() {
int
num = 5;
if
(num == 1) {
printf("Number
is 1\n");
} else if
(num == 2) {
printf("Number
is 2\n");
} else if (num
== 3)
{
printf("Number
is 3\n");
} else
{
printf("Number
is not 1, 2, or 3\n");
}
return
0;
}
In this example, the program checks the value of the `num`
variable and prints a message based on its value. Since `num` is 5, the output
will be "Number is not 1, 2, or 3."
You can use `else if` statements to evaluate
multiple conditions in sequence.
#include <stdio.h>
int main() {
int x = 3;
if
(x > 5)
{
printf("x
is greater than 5.\n");
}
else if (x == 5)
{
printf("x is equal to
5.\n");
} else
{
printf("x
is less than 5.\n");
}
return
0;
}
Output:
x is less than 5.
5.
nested if Statement: In C programming, you can use nested if statements to
create complex conditional branching logic. Nested if statements involve placing
one or more if statements inside another if statement's block. This allows you
to check multiple conditions in a hierarchical manner.
Here's the basic syntax
and an example of nested if statements in C:
if (condition1) {
//
Code to execute if condition1 is true
if
(condition2) {
// Code to execute if both condition1 and
condition2 are true
}
else
{
//
Code to execute if condition1 is true, but condition2 is false
}
}
else {
// Code to execute if condition1
is false
}
Here's a simple example to illustrate the concept:
#include <stdio.h>
int
main() {
int
num = 10;
if
(num > 0) {
printf("num
is positive\n");
if
(num % 2 == 0) {
printf("num
is even\n");
}
else
{
printf("num is
odd\n");
}
}
else {
printf("num
is not positive\n");
}
return 0;
}
In this example:
1. The first `if` statement checks if `num`
is greater than 0.
2. If `num` is greater than 0, it enters
the inner `if-else` block to check if `num` is even or odd.
3. If `num` is not greater than 0, it goes
to the `else` block of the outer `if` statement.
Nested if statements can be used to create more complex
conditions and execute different code blocks based on various combinations of
conditions. Just be careful to maintain proper indentation and structure to
ensure code readability.
7.
switch Statement: A switch statement in
C is a control statement that allows you to perform different actions based on
the value of a variable or an expression. It provides a way to replace multiple
`if-else if-else` constructs when you have a single variable to test against
multiple possible values. The switch statement is often more efficient and
easier to read when dealing with such situations.
The basic syntax of a switch statement in C is as follows:
switch (expression) {
case
value1:
//
Code to execute if expression equals value1
break;
case
value2:
//
Code to execute if expression equals value2
break;
//
Additional cases...
default:
// Code to execute if expression does not
match any of the above cases
}
Here's how a
switch statement works:
1. The `expression` is evaluated, and its value is compared
to the values in each `case` label sequentially.
2. If a match is found between the `expression` value and a
`case` label value, the code block associated with that case is executed. The
`break` statement is used to exit the switch block once a case is executed.
3. If no match is found, the code block associated with the
`default` case (if present) is executed. The `default` case is optional and
serves as a catch-all for values that don't match any of the defined cases.
Here's an example
of a switch statement in C:
#include <stdio.h>
int main() {
int
day = 3;
switch
(day) {
case 1:
printf("Monday\n");
break;
case
2:
printf("Tuesday\n");
break;
case
3:
printf("Wednesday\n");
break;
case
4:
printf("Thursday\n");
break;
case
5:
printf("Friday\n");
break;
default:
printf("Weekend\n");
}
return
0;
}
In this example, the value of the variable `day` is compared
to the cases, and the corresponding code block for "Wednesday" is
executed because `day` has the value 3.
Note that it's essential to include a `break` statement
after each case to prevent "fall-through." Fall-through happens when
the code execution continues to the next case even after a match. This can be
useful in some cases, but it's usually a source of bugs if not handled
intentionally.
Boolean Operator
In C programming, boolean operators are used to perform logical
operations on boolean values, which can be either true or false. These
operators are typically used in conditional statements and loops to control the
flow of a program based on certain conditions. C provides three main boolean
operators: AND, OR, and NOT. Here's an explanation of each of them:
1. Logical AND
(&&):
- Syntax: `expr1
&& expr2`
- Description: The
logical AND operator returns true if both `expr1` and `expr2` are true. If
either `expr1` or `expr2` (or both) is false, the result is false.
Example:
if (x > 5 && y < 10) {
// Code executes if both conditions are
true
}
2. Logical OR (||):
- Syntax: `expr1
|| expr2`
- Description: The
logical OR operator returns true if either `expr1` or `expr2` (or both) is
true. It only returns false if both `expr1` and `expr2` are false.
Example:
if (x == 0 || y == 0) {
// Code executes if either condition is
true
}
3. Logical NOT (!):
- Syntax: `!expr`
- Description: The
logical NOT operator is a unary operator that reverses the boolean value of
`expr`. If `expr` is true, `!expr` will be false, and if `expr` is false,
`!expr` will be true.
Example:
if (!flag) {
// Code executes if flag is false
}
These boolean operators are commonly used in
conditional statements (such as `if`, `while`, and `for` loops) to make
decisions based on the truth or falsity of certain conditions. They allow you
to create complex logical expressions by combining simple conditions. It's
essential to understand how these operators work to write efficient and
effective C programs with proper control flow.
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