Module 2: Chapter 3 — Statements

True and False in C

• In C, conditional expressions decide what action a program should take.
• A condition can be either true or false.
• True: Any nonzero value (positive or negative).
• False: The value 0.
• This rule makes C programs faster and more efficient.

Example:

Selection Statements

Introduction to Decision Control / Branching Statements

• Selection or branching statements allow the program to transfer control from one part of the code to another.
• This transfer can happen with or without a condition.
• These statements help make decisions during program execution.

Types of Branching Statements

• Conditional Branch Statements
• Unconditional Branch Statements

(i) Conditional Branch Statements

These statements transfer control based on a specific condition. If the condition is true, one block executes; otherwise, another may.

• Simple if - One-way selection
• if-else - Two-way selection
• Nested if - Multi-way selection
• else-if ladder - Multi-way selection
• switch - Multi-way selection

(ii) Unconditional Branch Statements

These statements transfer control unconditionally, without checking any condition.

• goto - Jumps to a labeled statement
• break - Exits a loop or switch
• continue - Skips to the next iteration of a loop
• return - Exits a function and optionally returns a value

if Statement

• The if statement executes a block of code only when a condition evaluates to true (nonzero).
• If the condition is false (0), the if block is skipped.
• Only one of if or else executes, never both.
• Used for "one-way decision" or "single alternative" choices.
• Syntax:
  
  if (condition) {
    // statements to execute if true
  }
  
• Rules:
  • The condition must be enclosed in parentheses.
  • Multiple statements must be enclosed in curly braces.
  • No semicolon is required after if (semicolon creates a null statement).

(if flow chart)

Example 1: Voting Eligibility

Example 2: Check Even or Odd

Example 3: Largest of Two Numbers

if-else Statement

• The if-else statement is used when there are two alternatives: one set of statements executes if the condition is true, and another set executes if it is false.
• Also called a "Two-way Decision or Selection Statement."
• Working Principle:
  • Test expression is evaluated first.
  • If true → execute Statement block 1; skip Statement block 2.
  • If false → execute Statement block 2; skip Statement block 1.
  • After either block executes, control passes to the next statement in sequence.
• Syntax:
  if (condition) {
   // Statements if true
  } else {
   // Statements if false
  }
  

(if else flow chart)

Example 1: Voting Eligibility

Example 2: Even or Odd

Example 3: Vowel or Consonant

Example 4: Leap Year Check

Cascaded if-else (if-else-if) Statement
if-else ladder

• Also called if-else-if ladder or else-if staircase due to its appearance.
• Used when multiple conditions must be checked in sequence; executes the first true condition and bypasses the rest.
• If none of the conditions are true, the final else executes (if present); otherwise, no action occurs.
• Special case of nested-if where nesting occurs only in the else part.
• Known as a Multi-way Decision or Selection Statement, useful when actions depend on ranges of values.
• Syntax
  if (condition1)
    statement1;
  else if (condition2)
    statement2;
  else if (condition3)
    statement3;
  ...
  else
    statementN;
  

(if-else-if-ladder flowchart)

Example: Grading System

Switch Statement

• The switch statement is a multi-way decision statement used to select one alternative among many.
• Evaluates an expression and compares its value with multiple case values.
• Executes the statements corresponding to the first matching case.
• default case executes if no match is found; it is optional.
• break statement ends a case and exits the switch; prevents fall-through.
• Syntax
  switch (expression) {
   case x:
     // code block
     break;
   case y:
     // code block
     break;
   default:
     // code block
  }
  

(switch-case flowchart)

Important: The Break Statement

Example 1: Display Grade

Example 2: Display Day of the Week

When to Use Which Conditional Statement?

Iterative Statements (Loops)

• Iterative statements, or loops, allow a set of statements to be executed repeatedly.
• Loops can run a specified number of times or until a certain condition is met.
• Also called looping constructs, repetitive statements, or loop control statements.
• Common types of loops in C:
  • for loop
  • while loop
  • do-while loop

for Loop (Counter-Controlled Loop)

• Executes a set of statements repeatedly for a specific number of times.
• Also called an entry-controlled loop or pretest loop.
• Syntax:
  for(initialization; test expression; increment/decrement) {
  statement1;
  statement2;
  statement3;
}
statement x;
• Working Principle:
  • Initialization: Set the starting value of loop variable.
  • Test expression: Evaluated before each iteration; if true, loop executes, else control moves out.
  • Increment/Decrement: Updates loop variable after each iteration.
• Infinite Loop: Omitting the test expression creates an infinite loop.
  Example: for(i=0;;i++)
{
...
}


(flowchart-for-Loop-Flow-Diagram)

Examples:

• Print natural numbers 1 to 10:
  for(int i=1;i<=10;i++) {
    printf("%d\n", i);
  }
• Print numbers 1 to n:
  int n; scanf("%d",&n);
  for(int i=1;i<=n;i++) {
    printf("%d\n", i);
  }
  
• Sum of 1+2+...+n:
  int sum=0,n; scanf("%d",&n);
  for(int i=1;i<=n;i++) {
   sum+=i;
  }
   printf("Sum=%d", sum);
• Generate n Fibonacci numbers:
  int f1=0,f2=1,f3,n,i;
  scanf("%d",&n);
  if(n==1)
   printf("%d",f1);
  else {
    printf("%d %d ", f1,f2);
    for(i=3;i<=n;i++) {
     f3=f1+f2;
     printf("%d ",f3);
     f1=f2;
     f2=f3;
   }
  }
• Print characters A to Z:
  for(char ch='A';ch<='Z';ch++) {
    printf("%c\t", ch);
  }
  
• Factorial of a number:
  int fact=1,n; scanf("%d",&n);
  for(int i=1;i<=n;i++) {
   fact*=i;
  }
  printf("Factorial=%d", fact);
  

while Loop

• Executes a set of statements repeatedly as long as a specified condition is true.
• Condition is checked before entering the loop → called an Entry-Controlled Loop.
• If the condition is false initially, the loop body is skipped.
• Control moves to the statement immediately after the loop once the condition becomes false.

(while-Loop)

while Loop - Syntax

Examples:

• Print natural numbers from 1 to 10:
  #include <stdio.h>
  void main() {
    int i=1;
    while(i<=10) {
      printf("%d\n", i);
      i++;
    }
  }
• Print numbers from 1 to n:
  int i=1, n;
  printf("Enter n: ");
  scanf("%d", &n);
  while(i<=n) {
    printf("%d\n", i); i++;
  }
• Print numbers from n to 1:
  int i=n;
  while(i>=1) {
    printf("%d\n", i);
    i--;
  }
  
• Sum of first 10 natural numbers:
  int i=1, sum=0;
  while(i<=10) {
    sum += i; i++;
  }
  printf("Sum=%d", sum);
  
• Print characters from A to Z:
  char ch='A';
  while(ch<='Z') {
    printf("%c\t", ch);
    ch++;
  }
• Factorial of a number:
  int fact=1, i=1, n;
  scanf("%d", &n);
  while(i<=n) {
    fact *= i;
    i++;
  }
  printf("Factorial=%d", fact);
  
• Check if a number is palindrome:
  int num, n, rev=0, digit;
  scanf("%d", &num);
  n=num;
  while(num! =0) {
    digit=num%10;
    rev=rev*10+digit;
    num/=10;
  }
  printf("Reversed=%d", rev);
  if(n==rev)
    printf("Palindrome");
  else
    printf("Not Palindrome");
  
• Find GCD and LCM of 2 numbers:
  int a,b,m,n,gcd,lcm,rem;
  scanf("%d %d", &a, &b);
  m=a;
  n=b;
  while(n! =0) {
    rem=m%n;
    m=n;
    n=rem;
  }
  gcd=m;
  lcm=(a*b)/gcd;
  printf("GCD=%d LCM=%d", gcd, lcm);

do-while Loop

• Executes a set of statements repeatedly at least once.
• The condition is tested after executing the loop body → called an Exit-Controlled Loop.
• Unlike for and while loops, which test the condition at the beginning, the do-while loop tests it at the end.
• The loop continues as long as the test expression is true.

Syntax:

Working Principle:

• The body of the loop executes once before checking the condition.
• After executing the body, the condition is evaluated to TRUE or FALSE.
• If TRUE → loop repeats; if FALSE → control exits to the statement after the loop.

(do-while-Loop)

(Flowchart-while-Loop)

Examples:

• Print natural numbers from 1 to 10:
  #include <stdio.h>
  void main() {
    int i = 1;
    do {
      printf("%d\n", i);
      i++;
    } while(i <= 10);
  }
• Print natural numbers from 1 to n:
  int i = 1, n;
  printf("Enter n: ");
  scanf("%d", &n);
  do {
    printf("%d\n", i);
    i++;
  } while(i <= n);
• Print numbers from n to 1:
  int n, i;
  printf("Enter n: ");
  scanf("%d", &n);
  i = n;
  do {
    printf("%d\n", i);
    i--;
  } while(i >= 1);
• Calculate sum of first 10 natural numbers:
  int i = 1, sum = 0;
  do {
    sum += i;
    i++;
  } while(i <= 10);
  printf("Sum = %d", sum);
• Find factorial of a given number:
  int fact = 1, i = 1, n;
  printf("Enter n: ");
  scanf("%d", &n);
  do {
    fact *= i;
    i++;
  } while(i <= n);
  printf("Factorial = %d", fact);
• Check if a number is palindrome:
  int num, n, rev = 0, digit;
  printf("Enter a number: ");
  scanf("%d", &num);
  n = num;
  do {
    digit = num % 10;
    rev = rev * 10 + digit;
    num /= 10;
  } while(num != 0);
  printf("Reversed = %d\n", rev);
  if(n == rev)
    printf("Palindrome");
  else
    printf("Not Palindrome");

Difference between while Loop and do-while Loop

Nested Loops

• A nested loop is a loop placed inside another loop.
• It can be used with any looping construct — while, do-while, or for.
• Nested loops are most commonly used with the for loop because it is easier to control.
• The inner loop controls the number of times a specific set of statements are executed.
• The outer loop controls how many times the entire loop structure is repeated.

(Flow chart of nested for loop)

Example:

Write a C program to print the following pattern:

Output:

In the above example:

• The outer loop (variable i) controls the number of rows.
• The inner loop (variable j) controls the number of columns (or stars printed per row).
• Each time the outer loop runs once, the inner loop runs multiple times until its condition fails.

Unconditional Branch Statements: break

• The break statement is used to terminate the execution of the nearest enclosing loop or switch statement.
• It is a jump statement that immediately transfers control to the statement following the loop or switch.
• In a switch statement, break prevents execution of subsequent cases.
• In loops (for, while, do-while), break exits the loop immediately, skipping remaining iterations.

(c-break-statement)

Syntax Examples:

• While loop:
  while(condition) {
    if(condition) break;
    ...
  }
  // Control transfers out of the while loop
• Do-while loop:
  do {
    if(condition) break;
    ...
  } while(condition);
  // Control transfers out of the do-while loop
• For loop:
  for(initialization; condition; increment) {
    if(condition) break;
    ...
  }
  // Control transfers out of the for loop

Example Program:

Print numbers 0 to 4 using break:

Output:

Unconditional Branch Statements: continue

• The continue statement is used to skip the current iteration of a loop and continue with the next iteration.
• It is used only inside loops (for, while, do-while).
• When continue is executed, the remaining statements in the loop body for that iteration are skipped.

(c-continue-statement)

Example Program:

Print numbers from 1 to 5, skipping 2:

Output:

Unconditional Branch Statements: goto Statement

• The goto statement is a jump statement that transfers program control to a labeled statement unconditionally.
• The specified label acts as a target and is identified by a valid variable name followed by a colon (:).
• The goto statement can cause both forward and backward jumps in a program.

Syntax:

(goto_statement)

Forward Jump: When control jumps to a label defined below the goto statement.

Backward Jump: When control jumps to a label defined above the goto statement.

Example Program:

Write a C program to calculate the sum of all numbers entered by the user.

Expression Statements (skip)

• An expression statement is simply a valid expression followed by a semicolon (;).
• Examples:
  • func(); → Function call
  • a = b + c; → Assignment statement
  • b + f(); → A valid but unusual statement (function f() is still evaluated)
  • ; → An empty or null statement
• Even seemingly strange expressions (like b + f();) are evaluated because the function might perform a useful action.
• Empty statements (;) do nothing but are syntactically valid.

Example Statements:

Block Statements (skip)

• Block statements (also called compound statements) are groups of related statements treated as a single unit.
• A block starts with a left brace { and ends with a matching right brace }.
• They are commonly used as multi-statement targets for control structures like if, for, and while.
• Blocks can also appear anywhere a normal statement is valid — even as a free-standing block.

Example Program:

Demonstration of a free-standing block statement: