pattern printing in c

Let’s do a quick crash revision on pattern printing in C. These are the classics interviewers love to throw at firmware/C devs.

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1. Right-Angle Triangle

#include <stdio.h>
int main() {
    int n = 5;
    for(int i=1;i<=n;i++){
        for(int j=1;j<=i;j++){
            printf("* ");
        }
        printf("\n");
    }
}

Output:

* 
* * 
* * * 
* * * * 
* * * * * 

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2. Inverted Triangle

#include <stdio.h>
int main() {
    int n = 5;
    for(int i=n;i>=1;i--){
        for(int j=1;j<=i;j++){
            printf("* ");
        }
        printf("\n");
    }
}

Output:

* * * * * 
* * * * 
* * * 
* * 
* 

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3. Pyramid

#include <stdio.h>
int main() {
    int n=5;
    for(int i=1;i<=n;i++){
        for(int s=1;s<=n-i;s++) printf(" ");  // spaces
        for(int j=1;j<=2*i-1;j++) printf("*");
        printf("\n");
    }
}

Output:

    *    
   ***   
  *****  
 ******* 
*********

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4. Diamond

#include <stdio.h>
int main() {
    int n=5;
    // upper half
    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");
    }
    // lower half
    for(int i=n-1;i>=1;i--){
        for(int s=1;s<=n-i;s++) printf(" ");
        for(int j=1;j<=2*i-1;j++) printf("*");
        printf("\n");
    }
}

Output:

    *    
   ***   
  *****  
 ******* 
*********
 ******* 
  *****  
   ***   
    *    

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5. Numbers Triangle

#include <stdio.h>
int main() {
    int n=5;
    for(int i=1;i<=n;i++){
        for(int j=1;j<=i;j++){
            printf("%d ", j);
        }
        printf("\n");
    }
}

Output:

1 
1 2 
1 2 3 
1 2 3 4 
1 2 3 4 5 

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Key takeaways for revision:

• Outer loop → rows (lines).
• Inner loop(s) → spaces & symbols/numbers.

• Think in terms of:

  1. Spaces before the symbol
  2. Printing the symbol (or number)

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