Star Triangle

Left Triangle

#include <stdio.h>

int main() {

    int n ;
    printf("Enter Number of rows:");
    scanf("%d", &n);

    for(int i=1; i<=n;i++){

        for(int j=1; j<=i; j++){
            printf("%c",64+j);
        }
        printf("\n");
    }

    return 0;
}

In C, braces { } group multiple statements into a block. You can skip them for a single statement, but using { } is safer and improves readability.

Right Triangle

#include <stdio.h>

int main() {

  int n;
  printf("Enter Number of rows:");
  scanf("%d", &n);

  for (int i = 1; i <= n; i++) {

    for (int s = n - i; s > 0; s--)
      printf(" ");
    for (int j = 1; j <= i; j++) {
      printf("*");
    }
    printf("\n");
  }

  return 0;
}

Upside Triangle

Left Upside down

#include <stdio.h>

int main() {

    int n ;
    printf("Enter Number of rows:");
    scanf("%d", &n);

    for(int i=n; i>0;i--){

        for(int j=1; j<=i; j++){
            printf("%c",64+j);
        }
        printf("\n");
    }

    return 0;
}

Right Upside down

#include <stdio.h>

int main() {

    int n ;
    printf("Enter Number of rows:");
    scanf("%d", &n);

    for(int i=n; i>0;i--){
        for(int s= n-i; s>0; s--)
            printf(" ");

        for(int j=1; j<=i; j++){
            printf("%c",64+j);
        }
        printf("\n");
    }

    return 0;
}