Else–if ladder in C - Step-by-Step Execution

Concept Flow - Else–if ladder

Start

↓

Check condition1

|Yes↓

Execute block1

↓

End

No↓

Check condition2

|Yes↓

Execute block2

↓

End

No↓

Check condition3

|Yes↓

Execute block3

↓

End

No↓

Execute else block

↓

End

The program checks conditions one by one from top to bottom. When a condition is true, it runs that block and skips the rest. If none are true, it runs the else block.

Execution Sample

C

int x = 15;
if (x < 10) {
    printf("Less than 10\n");
} else if (x < 20) {
    printf("Between 10 and 19\n");
} else {
    printf("20 or more\n");
}

This code checks the value of x and prints which range it falls into using an else-if ladder.

Execution Table

Step	Condition Checked	Condition Result	Action Taken	Output
1	x < 10	False	Skip block
2	x < 20	True	Execute block	Between 10 and 19
3	Else block	Skipped	Skip block
4	End	-	Exit ladder

💡 Condition x < 20 is True, so that block runs and ladder ends.

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
x	15	15	15	15

Key Moments - 2 Insights

Why does the program skip the else block after a true condition?

Once a true condition is found and its block runs (see Step 2 in execution_table), the else-if ladder ends immediately, so the else block is skipped.

What happens if all conditions are false?

If all conditions are false (like Step 1 and Step 2 false), the else block runs as a fallback (not shown in this example but explained in the flow).

Visual Quiz - 3 Questions

Look at the execution_table, what is the result of the first condition check?

A False

B True

C Skipped

D Error

💡 Hint

Check Step 1 row under 'Condition Result' column in execution_table.

At which step does the program print output?

A Step 1

B Step 3

C Step 2

D Step 4

💡 Hint

Look for the 'Output' column in execution_table where text appears.

If x was 25, which block would run?

A First if block

B Else block

C Second else-if block

D No block runs

💡 Hint

Refer to the concept_flow and think what happens when all conditions are false.

Concept Snapshot

Else–if ladder syntax:
if (condition1) {
  // block1
} else if (condition2) {
  // block2
} else {
  // else block
}

Checks conditions top-down, runs first true block, else runs if none true.

Full Transcript

This example shows how an else-if ladder works in C. The program checks each condition in order. If a condition is true, it runs that block and skips the rest. If none are true, it runs the else block. Here, x is 15. First condition x < 10 is false, so it skips. Second condition x < 20 is true, so it prints 'Between 10 and 19' and ends. The else block is skipped. Variables stay the same throughout. This helps decide between multiple choices step-by-step.

Practice

1. What does an else-if ladder do in C programming?

easy

A. Checks multiple conditions one by one and executes the first true block

B. Runs all conditions regardless of their truth value

C. Only executes the last condition in the ladder

D. Skips all conditions and runs the else block always

Solution

1. Step 1: Understand the purpose of else-if ladder

   An else-if ladder is used to check multiple conditions sequentially.

2. Step 2: Identify how conditions are executed

   Only the first condition that is true will have its block executed, and the rest are skipped.

3. Final Answer:

   Checks multiple conditions one by one and executes the first true block -> Option A

4. Quick Check:

   Else-if ladder = first true condition runs [OK]

Hint: Remember: else-if stops at first true condition [OK]

Common Mistakes:

• Thinking all conditions run regardless
• Believing else runs always
• Confusing else-if with multiple ifs

2. Which of the following is the correct syntax for an else-if ladder in C?

easy

A. if(condition) { } else(condition) { } else if { }

B. if(condition) { } else if(condition) { } else { }

C. if(condition) { } else if { } else(condition) { }

D. if(condition) { } else if(condition) { } else if

Solution

1. Step 1: Review correct else-if syntax

   The else-if ladder uses: if(condition) { } else if(condition) { } else { }.

2. Step 2: Check each option for syntax errors

   if(condition) { } else if(condition) { } else { } matches correct syntax; others have misplaced else or missing conditions.

3. Final Answer:

   if(condition) { } else if(condition) { } else { } -> Option B

4. Quick Check:

   Correct else-if syntax = if(condition) { } else if(condition) { } else { } [OK]

Hint: else if always needs a condition in parentheses [OK]

Common Mistakes:

• Writing else with a condition
• Omitting parentheses in else-if
• Ending else-if without braces

3. What will be the output of the following C code?

int x = 15;
if (x < 10) {
  printf("Less than 10\n");
} else if (x < 20) {
  printf("Less than 20\n");
} else {
  printf("20 or more\n");
}

medium

A. Less than 20

B. 20 or more

C. Less than 10

D. No output

Solution

1. Step 1: Evaluate first condition (x < 10)

   x is 15, which is not less than 10, so this block is skipped.

2. Step 2: Evaluate second condition (x < 20)

   15 is less than 20, so this block runs and prints "Less than 20".

3. Final Answer:

   Less than 20 -> Option A

4. Quick Check:

   15 < 20 = true, prints "Less than 20" [OK]

Hint: Check conditions top to bottom, first true runs [OK]

Common Mistakes:

• Choosing first condition without checking value
• Assuming else always runs
• Confusing output strings

4. Find the error in this else-if ladder code snippet:

int num = 5;
if (num > 10)
  printf("Greater than 10\n");
else if num > 0
  printf("Positive number\n");
else
  printf("Zero or negative\n");

medium

A. Missing semicolon after printf statements

B. else cannot be used without if

C. Incorrect variable name used

D. Missing parentheses around condition in else-if

Solution

1. Step 1: Check syntax of else-if condition

   In C, else-if condition must be inside parentheses: else if (condition).

2. Step 2: Identify the error in given code

   Code has else if num > 0 without parentheses, causing syntax error.

3. Final Answer:

   Missing parentheses around condition in else-if -> Option D

4. Quick Check:

   else-if needs parentheses [OK]

Hint: Always put conditions in parentheses after else if [OK]

Common Mistakes:

• Forgetting parentheses in else-if
• Missing semicolons after printf
• Misusing else without if

5. You want to write a program that prints "Child" if age < 13, "Teen" if age is between 13 and 19 inclusive, "Adult" if age is between 20 and 59 inclusive, and "Senior" if age is 60 or more. Which else-if ladder correctly implements this?

hard

A. if (age < 13) { printf("Child\n"); } else if (age < 20) { printf("Teen\n"); } else if (age < 59) { printf("Adult\n"); } else { printf("Senior\n"); }

B. if (age <= 13) { printf("Child\n"); } else if (age < 19) { printf("Teen\n"); } else if (age < 59) { printf("Adult\n"); } else { printf("Senior\n"); }

C. if (age <= 12) { printf("Child\n"); } else if (age <= 19) { printf("Teen\n"); } else if (age <= 59) { printf("Adult\n"); } else { printf("Senior\n"); }

D. if (age < 13) { printf("Child\n"); } else if (age < 19) { printf("Teen\n"); } else if (age <= 59) { printf("Adult\n"); } else { printf("Senior\n"); }

Solution

1. Step 1: Analyze age ranges for each category

   Child: age < 13 means age ≤ 12; Teen: 13 to 19 inclusive; Adult: 20 to 59 inclusive; Senior: 60 or more.

2. Step 2: Check each option's conditions

   if (age <= 12) { printf("Child\n"); } else if (age <= 19) { printf("Teen\n"); } else if (age <= 59) { printf("Adult\n"); } else { printf("Senior\n"); } correctly uses age ≤ 12 for Child, ≤ 19 for Teen, ≤ 59 for Adult, else Senior.

3. Final Answer:

   if (age <= 12) { printf("Child\n"); } else if (age <= 19) { printf("Teen\n"); } else if (age <= 59) { printf("Adult\n"); } else { printf("Senior\n"); } -> Option C

4. Quick Check:

   Correct age ranges with inclusive bounds = if (age <= 12) { printf("Child\n"); } else if (age <= 19) { printf("Teen\n"); } else if (age <= 59) { printf("Adult\n"); } else { printf("Senior\n"); } [OK]

Hint: Use inclusive bounds carefully in else-if conditions [OK]

Common Mistakes:

• Using wrong comparison operators
• Overlapping or missing age ranges
• Incorrect boundary values