Goto statement overview in C - Step-by-Step Execution

Concept Flow - Goto statement overview

Start

↓

Execute statements

↓

Check for goto

↓

Jump to label

↓

End

The program runs statements in order, but when it hits a goto, it jumps to a labeled spot and continues from there.

Execution Sample

C

int main() {
  int x = 0;
  if (x == 0) goto skip;
  x = 1;
  skip:
  return x;
}

This code uses goto to jump over the assignment x = 1 if x is 0, then returns x.

Execution Table

Step	Line	Action	Variable x	Notes
1	int x = 0;	Initialize x to 0	0	x set to 0
2	if (x == 0) goto skip;	Check if x is 0	0	Condition true, jump to label skip
3	skip:	Label reached	0	Jumped here, skip x=1
4	return x;	Return x value	0	Function returns 0
5	-	End of program	0	Program ends

💡 Program ends after returning x, which is 0 because assignment x=1 was skipped

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
x	undefined	0	0	0	0

Key Moments - 2 Insights

Why does the assignment x = 1 not happen?

Because at step 2 in the execution_table, the condition x == 0 is true, so the goto jumps directly to the label 'skip', skipping the assignment line.

What happens if the goto condition is false?

If the condition was false, the program would continue normally without jumping, executing the assignment x = 1 before reaching the label.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of x after step 3?

A undefined

B 0

C 1

D 2

💡 Hint

Check the 'Variable x' column at step 3 in the execution_table.

At which step does the program jump to the label 'skip'?

A Step 3

B Step 1

C Step 2

D Step 4

💡 Hint

Look at the 'Action' column in the execution_table for the goto decision.

If the condition in step 2 was false, what would be the value of x at the end?

A 1

B 0

C undefined

D 2

💡 Hint

If no jump occurs, the assignment x=1 would run before return.

Concept Snapshot

Goto statement overview in C:
- Syntax: goto label;
- Execution jumps to the label anywhere in the function
- Labels end with a colon (label:)
- Use carefully to avoid confusing flow
- Skips normal sequential execution
- Useful for simple jumps or error handling

Full Transcript

This example shows how the goto statement works in C. The program starts by setting x to 0. Then it checks if x equals 0. Since it does, the program jumps to the label 'skip', skipping the assignment x = 1. Finally, it returns x, which is still 0. The execution table shows each step and variable values. The variable tracker confirms x stays 0 throughout. Beginners often wonder why the assignment is skipped; it's because of the jump at step 2. If the condition was false, the program would run the assignment normally. The goto statement lets you jump to a labeled spot in the code, changing the normal flow.

Practice

1. What does the goto statement do in C programming?

easy

A. It jumps to a labeled part of the code within the same function.

B. It creates a new function.

C. It declares a variable.

D. It ends the program immediately.

Solution

1. Step 1: Understand the purpose of goto

   The goto statement is used to jump to a specific label inside the same function.

2. Step 2: Compare with other options

   Other options describe unrelated actions like creating functions or ending programs, which goto does not do.

3. Final Answer:

   It jumps to a labeled part of the code within the same function. -> Option A

4. Quick Check:

   goto jumps to label [OK]

Hint: Remember: goto jumps only inside the same function [OK]

Common Mistakes:

• Thinking goto can jump between functions
• Confusing goto with function calls
• Believing goto ends the program

2. Which of the following is the correct syntax to use goto in C?

easy

A. goto: label_name;

B. goto(label_name);

C. goto label_name;

D. goto = label_name;

Solution

1. Step 1: Recall correct goto syntax

   The correct syntax is simply goto label_name; without parentheses or equals sign.

2. Step 2: Check other options for syntax errors

   The other options use invalid syntax: one with a colon after goto, one with parentheses, and one with an equals sign.

3. Final Answer:

   goto label_name; -> Option C

4. Quick Check:

   Correct syntax is goto label; [OK]

Hint: Use 'goto label;' without parentheses or equals [OK]

Common Mistakes:

• Adding parentheses after goto
• Using equals sign with goto
• Writing colon after goto

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

int main() {
    int x = 0;
    start:
    x++;
    if (x < 3) goto start;
    printf("%d", x);
    return 0;
}

medium

A. 3

B. 0

C. 1

D. Infinite loop

Solution

1. Step 1: Trace the loop with goto

   The label start is before x++. The code increments x, then checks if x < 3. If yes, it jumps back to start.

2. Step 2: Count increments until condition fails

   x starts at 0, increments to 1, 2, then 3. When x is 3, condition x < 3 is false, so it stops looping and prints 3.

3. Final Answer:

   3 -> Option A

4. Quick Check:

   Loop increments x to 3 before printing [OK]

Hint: Count increments until condition fails [OK]

Common Mistakes:

• Thinking it prints 0 or 1
• Assuming infinite loop without checking condition
• Confusing label position

4. Identify the error in this C code using goto:

int main() {
    goto end;
    printf("Hello");
    end:
    return 0;
}

medium

A. Cannot jump over variable declarations.

B. No error; code runs and prints nothing.

C. Label 'end' is not defined.

D. Syntax error in goto statement.

Solution

1. Step 1: Check label definition and usage

   The label end is defined after the goto statement, so jumping to it is valid.

2. Step 2: Analyze program flow

   The program jumps to end, skipping the printf. So it prints nothing and returns 0 without error.

3. Final Answer:

   No error; code runs and prints nothing. -> Option B

4. Quick Check:

   Jumping to label after goto is allowed [OK]

Hint: Jumping forward to label is allowed; no error [OK]

Common Mistakes:

• Thinking label must be before goto
• Expecting output when skipped
• Assuming syntax error in goto

5. How can goto be used to break out of nested loops in C? Choose the best example.

hard

A. Use goto to jump to a label inside the inner loop.

B. Use goto to jump to a label after both loops finish.

C. Use goto to restart the inner loop from the beginning.

D. Use goto inside inner loop to jump to a label outside both loops.

Solution

1. Step 1: Understand nested loops and breaking out

   Normally, break exits only one loop. To exit multiple loops, goto can jump to a label after all loops.

2. Step 2: Identify correct usage of goto

   Using goto inside the inner loop to jump outside both loops immediately breaks out of all loops.

3. Final Answer:

   Use goto inside inner loop to jump to a label outside both loops. -> Option D

4. Quick Check:

   Goto jumps out of nested loops [OK]

Hint: Use goto to jump outside nested loops for quick exit [OK]

Common Mistakes:

• Using goto to restart loops instead of exit
• Jumping to label inside loops only
• Thinking break exits all loops