Printing triangle in C

Question

I am new to C and I have this program where I am trying to print a triangle based on its height as such:

 /\
/__\

So if the height is 2, then there are 2 of '/', '\' and '_'.

So I have written these chunk of codes:

#include <stdio.h>
int main(void)
{
    int noOfRows; 
    printf("Enter height: ");
    scanf("%d", &noOfRows);

    int counter, rowNumber;
    for (rowNumber = 0 ; rowNumber < noOfRows; rowNumber++)
    {
        // For each row, insert numberOfRows - N spaces before printing
        for (counter = 0 ; counter < noOfRows- rowNumber ; counter++)
            printf(" ");

        // For each row, print N times the character
            printf("/");

        for (counter = 0; counter < noOfRows; counter++)
            printf("\\");

        printf(" ");

        printf("\n");
    }

    return 0;
}

However it is giving me an output of such when I enter 3 as the height.

  /\\\
 /\\\
/\\\

I want to get the '\' with more space as each new row comes up but I am not sure how the for loop should be modified such that the triangle is formed correctly. Please let me know if I should add anymore question to make it clearer.

I made changes to the code and currently have this:

#include <stdio.h>
int main(void)
{
    int noOfRows; 
    printf("Enter height: ");
    scanf("%d", &noOfRows);

    int counter, rowNumber;
    for (rowNumber = 0 ; rowNumber < noOfRows; rowNumber++)
    {
        // For each row, insert numberOfRows - N spaces before printing
        for (counter = 0 ; counter < noOfRows- rowNumber ; counter++)
            printf(" ");

        // For each row, print N times the character
            printf("/");

        for (counter = 0 ; counter < rowNumber ; counter++)
            if(rowNumber >= 1)  
                for(int j=0; j<counter +1; j++)
                    printf(" ");

        if(rowNumber != 0)
            printf(" ");

            printf("\\");

        printf("\n");
    }

    return 0;
}

and now my current output is as such:

Height: 3
  /\
 /  \
/    \

Height: 5

    /\
   /  \
  /    \
 /       \
/           \

What did I do wrong in the code that is making some of the '\' go even further away?

Is this your college assignment? I suggest you to be more patience and try to solve this on your own, it will give you more pleasure if you solve it without taking anyone's help. Otherwise someone will definitely answer the trick with loops and print statement. — Gaurav Pathak, Mar 25 '17 at 05:56
Why are you printing `\\ ` in a loop? There's only one of those on each line. You need a loop to print spaces between `/` and `\\ `, similar to the loop you used to print the spaces before `/`. — Barmar, Mar 25 '17 at 05:59
And on the last line you need to print `_` instead of spaces. — Barmar, Mar 25 '17 at 06:00
@Barmar thank you, I took your suggestion and edited the code, see above where I posted the edited version of the code now. — Amy, Mar 25 '17 at 06:36

score 1 · Answer 1 · answered Mar 25 '17 at 07:12

@Barmar's idea is true and anymore you don't need if(rowNumber != 0) printf(" ");

Fullcode:

#include <stdio.h>
int main(void)
{
    int noOfRows; 
    printf("Enter height: ");
    scanf("%d", &noOfRows);
    int counter, rowNumber;
    for (rowNumber = 0 ; rowNumber < noOfRows; rowNumber++)    {

        for (counter = 0 ; counter < noOfRows- rowNumber ; counter++)
            printf(" ");        
            printf("/");
        for (counter = 0 ; counter < rowNumber ; counter++)
            if(rowNumber >= 1)  
                for (counter = 0; counter < rowNumber*2; counter++) {
        if (rowNumber == noOfRows-1) {
        printf("_");
        } else {
        printf(" ");
        }
        }
        printf("\\");
        printf("\n");
    }

}

score 1 · Accepted Answer · answered Mar 25 '17 at 07:20

You can use only two loop to print this pattern by using if else. in if else you can use multiple condition for space, backslash,forward-slash and underscore.

1 #include<stdio.h>
  2 
  3 int main()
  4 {
  5         int n;
  6         int i,j,k;
  7         printf("Enter hight of trangle\n");
  8         scanf("%d",&n);
  9         for(i=0;i<n;i++,printf("\n"))
 10         {
 11                 for(j=-n;j<=n;j++)
 12                 {
 13                         if(j<0) k=-j;
 14                         else    k=j;
 15 
 16                         if(j==0);
 17                         else if((j<0)&&(k==(i+1)))
 18                                 printf("/");
 19                         else if((j>0)&&(k==(i+1)))
 20                                 printf("\\");
 21                         else if((i+1)==n)
 22                                 printf("_");
 23                         else
 24                                 printf(" ");
 25                 }
 26         }
 27 }

Thank you, these set of codes worked in getting the single triangle :) — Amy, Mar 25 '17 at 23:48

score 0 · Answer 3 · answered Mar 25 '17 at 06:40

You don't need two nested loops to print the spaces between / and \\. It should just print rowNumber*2 spaces.

for (counter = 0; counter < rowNumber*2; counter++) {
    printf(" ");
}

You don't need to test if (rowNumber >= 1), because when it's 0 the loop ends immediately.

However, you do need a check for the last row, because you're supposed to print _ instead of space. So it should be:

for (counter = 0; counter < rowNumber*2; counter++) {
    if (rowNumber == noOfRows-1) {
        printf("_");
    } else {
        printf(" ");
    }
}

Thanks, I made the changes to the code and now I am able to print the single triangle!!! :) — Amy, Mar 25 '17 at 23:49

score 0 · Answer 4 · answered Mar 25 '17 at 17:06

Alternatively, you can abstract the repetitive printing of chars as:

// print_char(n,c) prints c n-times.
void print_char(int n, char c) {
  for (int i = 0; i < n; ++i) {
    printf("%c", c);
  }
}

so that you only have to keep track of one for loop when constructing the triangle as:

void print_triangle(int height) {
  for (int i = 1; i <= height; ++i) {
    print_char(height-i, ' ');               // print leading empty spaces
    printf("/");                             // print forward slash
    if (i == height) {                       // print middle dashes/spaces
      print_char((height-1)*2, '_');         //             <--|      |
    } else {                                 //                       |
      print_char((i-1)*2, ' ');              //             <---------|
    }
    printf("\\\n");                          // print backslash
  }
}

For example,

int main(void) {
  int height;
  printf("Enter height: ");
  if (scanf("%d", &height) != 1) {
    // handle error if scanf fails
  }
  print_triangle(height);
  return 0;
}

and then,

$ Enter height: 1
/\
$ Enter height: 5
    /\
   /  \
  /    \
 /      \
/________\

Printing triangle in C

4 Answers4