> ## Documentation Index
> Fetch the complete documentation index at: https://learn.acadlink.app/llms.txt
> Use this file to discover all available pages before exploring further.
# Control Structure
> Decision-making, looping, and jumping statements in C
# Control Structure in C
**Control structures** determine how a program runs its instructions. They allow the program to make decisions, repeat steps, or jump to different parts of the code based on conditions.
A control structure is a combination of:
* **Decision-making statements** — `if`, `else`, `switch`
* **Looping statements** — `for`, `while`, `do-while`
* **Jumping statements** — `break`, `continue`, `goto`, `return`
***
## Decision-Making Statements
### 1. `if` Statement
Executes a block only when the condition is true.
```c theme={null}
if (condition) {
// executes if condition is true
}
```
**Example:**
```c theme={null}
#include
int main() {
int age = 18;
if (age >= 18) {
printf("Eligible to Vote\n");
printf("Welcome\n");
}
return 0;
}
```
Output: `Eligible to Vote` and `Welcome`
Without curly braces, only the **immediately following** line is part of the `if`. The rest always executes.
***
### 2. `if-else` Statement
```c theme={null}
if (condition) {
// true block
} else {
// false block
}
```
**Example:**
```c theme={null}
int num = 5;
if (num % 2 == 0) {
printf("Even number");
} else {
printf("Odd number");
}
// Output: Odd number
```
***
### 3. `if-else if-else` Ladder
Check multiple conditions in sequence:
```c theme={null}
int marks = 72;
if (marks >= 90) {
printf("Grade A\n");
} else if (marks >= 75) {
printf("Grade B\n");
} else if (marks >= 50) {
printf("Grade C\n");
} else {
printf("Fail\n");
}
// Output: Grade C
```
***
### 4. Nested `if`
An `if` inside another `if`:
```c theme={null}
int age = 25;
char citizen = 'Y';
if (age >= 18) {
if (citizen == 'Y') {
printf("You can vote in India.\n");
}
}
```
***
### 5. `switch-case`
Use when choosing one option from many based on a single value:
```c theme={null}
switch (expression) {
case constant1:
// code
break;
case constant2:
// code
break;
default:
// runs if no case matches
}
```
**Rules:**
* Expression must be `int`, `char`, or `enum` (NOT `float`)
* Case labels must be constants
* `break` stops the switch from falling through to the next case
* `default` is optional
**Example:**
```c theme={null}
#include
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;
}
// Output: Wednesday
```
**Fall-through (no break):**
```c theme={null}
int x = 2;
switch (x) {
case 1: printf("One\n");
case 2: printf("Two\n"); // no break → continues
case 3: printf("Three\n"); break;
}
// Output:
// Two
// Three
```
***
## Looping Statements
### `while` Loop
Checks condition **before** executing the body:
```c theme={null}
int i = 1;
while (i <= 5) {
printf("%d\n", i);
i++;
}
```
### `do-while` Loop
Executes the body **at least once**, then checks condition:
```c theme={null}
int i = 1;
do {
printf("%d\n", i);
i++;
} while (i <= 5);
```
### `for` Loop
Best when the number of iterations is known:
```c theme={null}
for (int i = 1; i <= 5; i++) {
printf("%d\n", i);
}
```
### Nested Loops
```c theme={null}
for (int i = 1; i <= 3; i++) {
for (int j = 1; j <= 3; j++) {
printf("%d %d\n", i, j);
}
}
```
### Infinite Loop
```c theme={null}
while (1) { printf("Running...\n"); }
for (;;) { printf("Running...\n"); }
```
***
## Jumping Statements
### `break`
Exits a loop or switch immediately:
```c theme={null}
for (int i = 1; i <= 5; i++) {
if (i == 3) break;
printf("%d\n", i);
}
// Output: 1 2
```
### `continue`
Skips the rest of the current iteration:
```c theme={null}
for (int i = 1; i <= 5; i++) {
if (i == 3) continue;
printf("%d\n", i);
}
// Output: 1 2 4 5
```
### `goto`
Transfers control to a labeled statement (use sparingly):
```c theme={null}
#include
int main() {
int num = 2;
if (num == 2) goto label;
printf("This will be skipped\n");
label:
printf("Jumped here using goto\n");
return 0;
}
// Output: Jumped here using goto
```
### `return`
Exits a function and optionally returns a value:
```c theme={null}
int add(int a, int b) {
return a + b;
}
int main() {
printf("%d\n", add(3, 4)); // Output: 7
return 0;
}
```
### `exit()`
Terminates the entire program immediately. Requires `#include `:
```c theme={null}
#include
#include
int main() {
printf("Start\n");
exit(0);
printf("This will not execute\n");
return 0;
}
// Output: Start
```