Control Statements in C

 

In C programming statements are usually grouped into categories based on what they do in a program.
Here’s a clear and simple breakdown.

Type of Statement	Examples	Purpose
Declaration	int x;	Reserve memory for variables
Input/Output	printf(), scanf()	Take input & display output
Expression	x = y + 5;	Perform operations
Conditional	if, switch	Make decisions
Looping	for, while	Repeat tasks
Jump	break, continue, return, goto	Used to jump to another part of the program

 

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1. Declaration Statements

These are statements used to declare variables, constants, arrays, or functions before you use them in a program.
They tell the compiler:

The name of the data

The type of data (integer, float, char, etc.)

Sometimes the initial value

Syntax :- data_type variable_name;

Or        data_type variable_name = value;

Examples

int age;               // Declaring an integer variable

float price;           // Declaring a floating-point variable

char grade;            // Declaring a character variable

int rollNo = 101;      // Declaring and initializing

const int MAX = 100;   // Declaring a constant

 These tell the compiler about the type and name of data we will use.

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2. Input/Output Statements

1. Formatted Output Statement — printf()

·        Used to display text, variables, and results in a controlled way.

·        Provided by the stdio.h library.

Syntax:

printf("format string", variable1, variable2, ...);

Common Format Specifiers for Output

Data Type	Format Specifier	Example Output
int	%d or %i	25
float	%f	3.140000
float (2 dp)	%.2f	3.14
char	%c	A
string	%s	Hello

Examples:

printf("Age: %d\n", 15);             // Integer output

printf("Price: %.2f\n", 45.678);     // Float with 2 decimal places

printf("Grade: %c\n", 'A');          // Character

printf("Name: %s\n", "Rahul");       // String

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2. Formatted Input Statement — scanf()

·        Used to read data entered by the user from the keyboard in a specific format.

·        Provided by the stdio.h library.

Syntax:

scanf("format string", &variable1, &variable2, ...);

& (address-of operator) is used before variable names in scanf() except for strings.

Common Format Specifiers for Input

Data Type	Format Specifier	Example Input
int	%d	25
float	%f	3.14
char	%c	A
string	%s	Hello

Examples:

int age;

scanf("%d", &age);    // Reads an integer

float price;

scanf("%f", &price);  // Reads a float

char grade;

scanf("%c", &grade);  // Reads a character

char name[20];

scanf("%s", name);    // Reads a string (no & for strings)

 

Unformatted Input & Output Statements in C

In C programming, unformatted I/O statements are used for simple character or string reading and writing without using format specifiers like %d, %f, etc.

They work directly with characters or strings and are also provided by the stdio.h library.

 

1. Unformatted Output Statements

(a) putchar()

Outputs a single character to the screen.

Syntax:

    putchar(character);

Example:

putchar('A');   // Displays: A

 

(b) puts()

Outputs a string followed by a newline (\n).

Syntax:

puts(string_variable);

Example:

char name[] = "Rahul";

puts(name);     // Displays: Rahul (then goes to next line)

 

2. Unformatted Input Statements

(a) getchar()

Reads a single character from the keyboard.

Syntax:

      variable = getchar();

Example:

char ch;

ch = getchar();   // User enters 'A'

 

(b) gets() (Not recommended in modern C because it is unsafe)

Reads a string (including spaces) until Enter is pressed.

Syntax:

gets(string_variable);

Example:

char name[20];

gets(name);      // User enters: Rahul Kumar

 gets() can cause memory overflow, so in modern C, fgets() is preferred.

 

3. Expression Statements

An expression is anything that produces a value — like a calculation, assignment, or function call.
Example:

1. Simple Expression Statements

Contain only one operation.

Examples:

x = 5;       // Simple assignment

count++;     // Increment

y--;         // Decrement

 

2. Complex Expression Statements

Contain multiple operations in the same statement.

Examples:

result = (a + b) * c;   // Arithmetic + assignment

x = y + z - w / 2;      // Multiple operators

sum = a++ + --b;        // Increment + addition

 

4. Control Statements

     Types of Control Statements

A. Conditional (Decision-making) Statements

Used to make decisions based on a condition (true or false).

1. if statement

if (marks >= 33)

    printf("Pass");

2. if...else statement

if (marks >= 33)

    printf("Pass");

else

    printf("Fail");

4. switch statement

switch (day) {

    case 1: printf("Monday"); break;

    case 2: printf("Tuesday"); break;

    default: printf("Invalid Day");

}

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B. Looping (Iteration) Statements

Used to repeat a block of code multiple times.

1. for loop

for (i = 1; i <= 5; i++)

    printf("%d\n", i);

2. while loop

i = 1;

while (i <= 5) {

    printf("%d\n", i);

    i++;

}

3. do...while loop

i = 1;

do {

    printf("%d\n", i);

    i++;

} while (i <= 5);

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C. Jump Statements

Used to jump to another part of the program.

1. break

for (i = 1; i <= 10; i++) {

    if (i == 5) break; // Exit loop

    printf("%d\n", i);

}

2. continue

for (i = 1; i <= 5; i++) {

    if (i == 3) continue; // Skip 3

    printf("%d\n", i);

}

3. goto

goto label;

printf("This will be skipped");

label:

printf("Jumped here");

4. return

return 0; // End function and return control