break, continue, and goto Statements

📖 Introduction

C provides three jump statements that alter the normal flow of control: break, continue, and goto. These statements allow you to exit loops early, skip iterations, or jump to specific locations in your code.

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🎯 Overview

                    Jump Statements
                          │
        ┌─────────────────┼─────────────────┐
        │                 │                 │
      break           continue            goto
        │                 │                 │
   ┌────┴────┐      ┌─────┴─────┐     ┌─────┴─────┐
   │ Exit    │      │ Skip to   │     │ Jump to   │
   │ loop or │      │ next      │     │ labeled   │
   │ switch  │      │ iteration │     │ statement │
   └─────────┘      └───────────┘     └───────────┘

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🔴 The break Statement

break immediately exits the innermost loop or switch statement.

Syntax:

break;

In Loops:

for (int i = 0; i < 10; i++) {
    if (i == 5) {
        break;  // Exit loop when i is 5
    }
    printf("%d ", i);
}
// Output: 0 1 2 3 4

Flowchart:

       ┌─────────────────┐
       │ i = 0           │
       └────────┬────────┘
                │
                ▼
       ┌─────────────────┐
   ┌──►│ i < 10?         │──No──► Exit
   │   └────────┬────────┘
   │            │ Yes
   │            ▼
   │   ┌─────────────────┐
   │   │ i == 5?         │──Yes──► break ──► Exit
   │   └────────┬────────┘
   │            │ No
   │            ▼
   │   ┌─────────────────┐
   │   │ printf(i)       │
   │   └────────┬────────┘
   │            │
   │            ▼
   │   ┌─────────────────┐
   │   │ i++             │
   │   └────────┬────────┘
   │            │
   └────────────┘

Common Use Cases:

1. Search and Exit:

int target = 42;
int index = -1;
int arr[] = {10, 20, 42, 50, 60};

for (int i = 0; i < 5; i++) {
    if (arr[i] == target) {
        index = i;
        break;  // Found! No need to continue
    }
}
printf("Found at index: %d\n", index);

2. Input Validation:

while (1) {  // Infinite loop
    int input;
    printf("Enter positive number (0 to exit): ");
    scanf("%d", &input);

    if (input == 0) {
        break;  // Exit on 0
    }

    if (input > 0) {
        printf("You entered: %d\n", input);
    }
}

3. Early Termination:

// Find first divisor
int num = 100;
for (int i = 2; i <= num; i++) {
    if (num % i == 0) {
        printf("First divisor: %d\n", i);
        break;
    }
}

break Only Exits One Level:

for (int i = 0; i < 3; i++) {
    for (int j = 0; j < 3; j++) {
        if (j == 1) {
            break;  // Only exits inner loop
        }
        printf("(%d, %d) ", i, j);
    }
    printf("\n");
}
// Output:
// (0, 0)
// (1, 0)
// (2, 0)

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🟡 The continue Statement

continue skips the rest of the current iteration and jumps to the next iteration.

Syntax:

continue;

Example:

for (int i = 0; i < 10; i++) {
    if (i % 2 == 0) {
        continue;  // Skip even numbers
    }
    printf("%d ", i);
}
// Output: 1 3 5 7 9

Flowchart:

       ┌─────────────────┐
       │ i = 0           │
       └────────┬────────┘
                │
                ▼
       ┌─────────────────┐
   ┌──►│ i < 10?         │──No──► Exit
   │   └────────┬────────┘
   │            │ Yes
   │            ▼
   │   ┌─────────────────┐
   │   │ i even?         │──Yes──► continue ──┐
   │   └────────┬────────┘                    │
   │            │ No                          │
   │            ▼                             │
   │   ┌─────────────────┐                    │
   │   │ printf(i)       │                    │
   │   └────────┬────────┘                    │
   │            │                             │
   │            ▼                             │
   │   ┌─────────────────┐                    │
   │   │ i++             │◄───────────────────┘
   │   └────────┬────────┘
   │            │
   └────────────┘

continue in Different Loop Types:

In for Loop:

for (int i = 0; i < 5; i++) {
    if (i == 2) continue;
    printf("%d ", i);
}
// Output: 0 1 3 4
// Note: i++ still executes after continue

In while Loop:

int i = 0;
while (i < 5) {
    i++;
    if (i == 3) continue;
    printf("%d ", i);
}
// Output: 1 2 4 5

⚠️ Careful with while:

int i = 0;
while (i < 5) {
    if (i == 2) {
        continue;  // BUG: i never incremented!
    }
    printf("%d ", i);
    i++;
}
// Infinite loop!

Common Use Cases:

1. Skip Invalid Data:

int data[] = {5, -1, 10, -2, 15, 0, 20};
int sum = 0;

for (int i = 0; i < 7; i++) {
    if (data[i] <= 0) {
        continue;  // Skip non-positive values
    }
    sum += data[i];
}
printf("Sum of positive: %d\n", sum);  // 50

2. Filter Processing:

char str[] = "Hello, World!";

printf("Letters only: ");
for (int i = 0; str[i] != '\0'; i++) {
    if (!((str[i] >= 'a' && str[i] <= 'z') ||
          (str[i] >= 'A' && str[i] <= 'Z'))) {
        continue;  // Skip non-letters
    }
    printf("%c", str[i]);
}
// Output: HelloWorld

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🔵 The goto Statement

goto transfers control to a labeled statement. Use with extreme caution!

Syntax:

goto label;

// ... code ...

label:
    // code at label

Example:

int i = 0;

loop:
    if (i >= 5) goto end;
    printf("%d ", i);
    i++;
    goto loop;

end:
    printf("\nDone!\n");
// Output: 0 1 2 3 4
// Done!

⚠️ Why goto is Discouraged

1. •Creates "spaghetti code" - hard to follow
2. •Breaks structured programming
3. •Difficult to debug
4. •Can jump over variable initializations
5. •Makes code maintenance harder

Acceptable Uses of goto:

1. Breaking Out of Nested Loops:

for (int i = 0; i < 10; i++) {
    for (int j = 0; j < 10; j++) {
        for (int k = 0; k < 10; k++) {
            if (condition) {
                goto found;  // Exit all loops
            }
        }
    }
}
found:
    printf("Exited all loops\n");

2. Error Handling with Cleanup:

int processFile() {
    FILE *file = fopen("data.txt", "r");
    if (!file) goto error_file;

    int *buffer = malloc(1000);
    if (!buffer) goto error_buffer;

    // Process file...

    // Success path
    free(buffer);
    fclose(file);
    return 0;

error_buffer:
    fclose(file);
error_file:
    return -1;
}

Alternatives to goto:

// Instead of goto for nested loops, use a flag:
int found = 0;
for (int i = 0; i < 10 && !found; i++) {
    for (int j = 0; j < 10 && !found; j++) {
        if (condition) {
            found = 1;
        }
    }
}

// Or extract to a function and use return:
void searchMatrix() {
    for (int i = 0; i < 10; i++) {
        for (int j = 0; j < 10; j++) {
            if (condition) {
                return;  // Exit function
            }
        }
    }
}

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⚖️ Comparison Table

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📊 Control Flow Summary

Normal loop flow:
┌─────────────────────────────────────────────┐
│  for (init; condition; update) {            │
│      if (x) break;     // Exit loop now     │
│      if (y) continue;  // Skip to update    │
│      // Normal code                         │
│  }                                          │
└─────────────────────────────────────────────┘

With goto (avoid):
┌─────────────────────────────────────────────┐
│  label:                                     │
│      // code                                │
│      if (x) goto label;  // Jump to label   │
└─────────────────────────────────────────────┘

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🎯 Best Practices

Do's:

1. •Use break to exit loops when target is found
2. •Use continue to skip unwanted iterations
3. •Keep loop logic simple and readable
4. •Consider extracting complex loops to functions

Don'ts:

1. •Don't use goto except for specific cleanup patterns
2. •Don't overuse break - consider restructuring
3. •Don't forget to update loop variables before continue in while
4. •Don't use break to exit from nested loops (use flags or functions)

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🔑 Key Takeaways

1. •break exits the innermost loop or switch immediately
2. •continue skips to the next loop iteration
3. •goto jumps to a label (avoid using it!)
4. •break and continue only affect one loop level
5. •Use flags or functions instead of goto for nested loops
6. •Be careful with continue in while loops

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⏭️ Next Topic

Continue to Nested Loops to learn about loops within loops.