C program to print pascal triangle

Write a C program to print pascal triangle up to n rows using loop. Logic to print Pascal triangle in C programming. How to print Pascal triangle of n rows using loop in C program.

Input rows: 5

    1
   1 1
  1 2 1
 1 3 3 1
1 4 6 4 1

Required knowledge

Basic C programming, For loop, While loop, Nested loop, Functions

Pascal Triangle

Pascal triangle is a triangular number pattern named after famous mathematician Blaise Pascal.

For example Pascal triangle with 6 rows.

Logic to print pascal triangle

To find n^th term of a pascal triangle we use following formula.

Where n is row number and k is term of that row.

Step by step descriptive logic to print pascal triangle.

1. Input number of rows to print from user. Store it in a variable say num.
2. To iterate through rows, run a loop from 0 to num, increment 1 in each iteration. The loop structure should look like for(n=0; n<num; n++).
3. Inside the outer loop run another loop to print terms of a row. Initialize the loop from 0 that goes to n, increment 1 in each iteration.
4. Inside the inner loop use formula term = fact(n) / (fact(k) * fact(n-k)); to print current term of pascal triangle.

   Here, fact() is a function defined to find factorial of a number.

Program to print Pascal triangle

/**
 * C program to print Pascal triangle up to n rows
 */

#include <stdio.h>

/* Function definition */
long long fact(int n);

int main()
{
    int n, k, num, i;
    long long term;

    /* Input number of rows */
    printf("Enter number of rows : ");
    scanf("%d", &num);

    for(n=0; n<num; n++)
    {
        /* Prints 3 spaces */
        for(i=n; i<=num; i++)
            printf("%3c", ' ');

        /* Generate term for current row */
        for(k=0; k<=n; k++)
        {
            term = fact(n) / (fact(k) * fact(n-k));

            printf("%6lld", term);
        }

        printf("\n");
    }

    return 0;
}

/**
 * Function to calculate factorial
 */
long long fact(int n)
{
    long long factorial = 1ll;
    while(n>=1)
    {
        factorial *= n;
        n--;
    }

    return factorial;
}

Let us take a note of the above program.

• The statement printf("%3c", ' '); is used to print 3 white spaces and is equivalent to printf("   ");.
• The statement printf("%6lld", term); prints the current term with 6 character width.
• To print a long long type value I have used %lld format specifier.
• In the fact() function I have added ll suffix while declaring long long factorial = 1ll;. Since 1 is an integer variable, hence to tell the compiler explicitly that store 1 as long long type I have added the suffix.
  

  Read more – Literals in C programming.

Enter number of rows : 10
                         1
                       1   1
                     1   2   1
                   1   3   3   1
                 1   4   6   4   1
               1   5  10  10   5   1
             1   6  15  20  15   6   1
           1   7  21  35  35  21   7   1
         1   8  28  56  70  56  28   8   1
       1   9  36  84 126 126  84  36   9   1

Happy coding 😉