Bytebook Compiler

Control Flow

Break, Continue & Pattern Programs

Control loops with break, continue and goto, then master nested loops through the star and number patterns every exam asks for.

5 min read8 runnable examples4-question quiz

break

break ends the nearest loop (or switch) immediately:

C
#include <stdio.h>

int main(void) {
    for (int i = 1; i <= 10; i++) {
        if (i == 6) break;
        printf("%d ", i);
    }
    printf("\nLoop ended early.\n");
    return 0;
}
Output
1 2 3 4 5 
Loop ended early.
Try it Yourself

continue

continue skips the rest of the current pass and jumps to the next one:

C
#include <stdio.h>

int main(void) {
    printf("Odd numbers below 12: ");
    for (int i = 1; i < 12; i++) {
        if (i % 2 == 0) continue;
        printf("%d ", i);
    }
    printf("\n");
    return 0;
}
Output
Odd numbers below 12: 1 3 5 7 9 11
Try it Yourself

Nested loops

A loop inside another loop runs its inner body rows × columns times. The outer loop usually picks the row; the inner loop prints the columns of that row. That is the whole secret of pattern programs.

C
#include <stdio.h>

int main(void) {
    for (int row = 1; row <= 3; row++) {
        for (int col = 1; col <= 4; col++)
            printf("(%d,%d) ", row, col);
        printf("\n");
    }
    return 0;
}
Output
(1,1) (1,2) (1,3) (1,4) 
(2,1) (2,2) (2,3) (2,4) 
(3,1) (3,2) (3,3) (3,4)
Try it Yourself

Pattern 1: right triangle

Row i has i stars.

C
#include <stdio.h>

int main(void) {
    int n = 5;
    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= i; j++)
            printf("* ");
        printf("\n");
    }
    return 0;
}
Output
* 
* * 
* * * 
* * * * 
* * * * *
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Pattern 2: number triangle and Floyd's triangle

C
#include <stdio.h>

int main(void) {
    int n = 4, k = 1;
    for (int i = 1; i <= n; i++) {          // 1 / 1 2 / 1 2 3 ...
        for (int j = 1; j <= i; j++) printf("%d ", j);
        printf("\n");
    }
    printf("\n");
    for (int i = 1; i <= n; i++) {          // Floyd: keep counting across rows
        for (int j = 1; j <= i; j++) printf("%-3d", k++);
        printf("\n");
    }
    return 0;
}
Output
1 
1 2 
1 2 3 
1 2 3 4 

1  
2  3  
4  5  6  
7  8  9  10
Try it Yourself

Pattern 3: pyramid

Each row needs spaces first, then stars. For n rows, row i has n - i spaces and 2i - 1 stars.

C
#include <stdio.h>

int main(void) {
    int n = 5;
    for (int i = 1; i <= n; i++) {
        for (int s = 1; s <= n - i; s++) printf(" ");
        for (int j = 1; j <= 2 * i - 1; j++) printf("*");
        printf("\n");
    }
    return 0;
}
Output
    *
   ***
  *****
 *******
*********
Try it Yourself

Pattern 4: diamond

A diamond is a pyramid followed by an upside-down pyramid:

C
#include <stdio.h>

int main(void) {
    int n = 4;
    for (int i = 1; i <= n; i++) {
        for (int s = 0; s < n - i; s++) printf(" ");
        for (int j = 0; j < 2 * i - 1; j++) printf("*");
        printf("\n");
    }
    for (int i = n - 1; i >= 1; i--) {
        for (int s = 0; s < n - i; s++) printf(" ");
        for (int j = 0; j < 2 * i - 1; j++) printf("*");
        printf("\n");
    }
    return 0;
}
Output
   *
  ***
 *****
*******
 *****
  ***
   *
Try it Yourself

Pattern 5: Pascal's triangle

Each number is the sum of the two above it. Using the formula C(i, j+1) = C(i, j) × (i − j) / (j + 1) we can print each row without storing earlier rows:

C
#include <stdio.h>

int main(void) {
    int n = 6;
    for (int i = 0; i < n; i++) {
        for (int s = 0; s < n - i - 1; s++) printf("  ");
        int c = 1;
        for (int j = 0; j <= i; j++) {
            printf("%4d", c);
            c = c * (i - j) / (j + 1);
        }
        printf("\n");
    }
    return 0;
}
Output
             1
           1   1
         1   2   1
       1   3   3   1
     1   4   6   4   1
   1   5  10  10   5   1
Try it Yourself

Test yourself

4 questions · pick an answer to check it instantly

  1. 1

    What does this print?

    C
    for (int i = 1; i <= 5; i++) {
    if (i == 3) continue;
    printf("%d", i);
}
  2. 2

    How many stars does this print in total?

    C
    for (int i = 1; i <= 4; i++)
    for (int j = 1; j <= i; j++)
        printf("*");
  3. 3

    In a 5-row centred pyramid, how many stars are on row 3?

  4. 4

    Which statement about break is true?

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