This document discusses nested loops in structured programming languages. It provides examples of nested for loops in C code, explaining how the inner loop executes fully for each pass of the outer loop. It also calculates the total number of iterations in nested loops. Examples are given of nested loops printing star and number patterns of different shapes based on a user-input integer.

1. Structured Programming Language
Nested Loop
Mohammad Imam Hossain,
Lecturer, CSE, UIU

2. Nested Loop
• A nested loop is a loop within a loop i.e.
an inner loop within the body of an outer
one.
• The first pass of the outer loop triggers
the inner loop, which executes to
completion.
• Then the second pass of the outer loop
triggers the inner loop again.
• This repeats until the outer loop finishes.

3. Nested for Loop
#include <stdio.h>
int main()
{
int n=3, m=5;
int cnt=0,i,j;
for(i=1;i<=n;i++){
for(j=1;j<=m;j++){
++cnt;
}
}
printf("inner loop iterates in total %d timesn",cnt);
return 0;
}
Trace
it……

4. Total no of Iterations
• When i=1, the inner loop executes m times
• When i=2, the inner loop executes m times
• .
• .
• .
• When i=n, the inner loop executes m times.
So total no of iterations = m + m + m+ … … … +m = n *m

5. Nested for Loop
Trace
it……
#include <stdio.h>
int main()
{
int n=10;
int cnt=0,i,j;
for(i=1;i<=n;i++){
for(j=1;j<=i;j++){
++cnt;
}
}
printf("inner loop iterates in total %d timesn",cnt);
return 0;
}

6. Total no of Iterations
• When i=1, the inner loop executes 1 times
• When i=2, the inner loop executes 2 times
• When i=3, the inner loop executes 3 times
• .
• .
• When i=n, the inner loop executes n times.
So total no of iterations = 1 + 2 + 3+ … … … +n
= n(n+1) / 2

7. Flow Chart of Nested Loop

8. Problem
• Input: n (integer)
• Output: the following shape when n=5
* * * * *
* * * * *
* * * * *
* * * * *
* * * * *

10. Problem
• Input: n (integer)
• Output: the following shape when n=5
* * * * *
* *
* *
* *
* * * * *

11. Problem
• Input: n (integer)
• Output: the following shape when n=5
* * * * *
* * * * *
* * * * *
* * * * *
* * * * *

12. Problem
• Input: n (integer)
• Output: the following shape when n=5
* * * * *
* *
* *
* *
* * * * *

13. Problem
• Input: n (integer)
• Output: the following shape when n=5
*
* *
* * *
* * * *
* * * * *

15. Problem
• Input: n (integer)
• Output: the following shape when n=5
*
* *
* * *
* * * *
* * * * *

16. Problem
• Input: n (integer)
• Output: the following shape when n=5
*
* *
* *
* *
* * * * *

17. Problem
• Input: n (integer)
• Output: the following shape when n=5
* * * * *
* * * *
* * *
* *
*

18. Problem
• Input: n (integer)
• Output: the following shape when n=5
* * * * *
* * * *
* * *
* *
*

19. Problem
• Input: n (integer)
• Output: the following shape when n=5
* * * * * * * * *
* * * * * * *
* * * * *
* * *
*

20. Problem
• Input: n (integer)
• Output: the following shape when n=5
1 2 3 4 5
2 3 4 5 6
3 4 5 6 7
4 5 6 7 8
5 6 7 8 9

21. Problem
• Input: n (integer)
• Output: the following shape when n=5
5 4 3 2 1
4 3 2 1
3 2 1
2 1
1

22. Problem
• Input: n (integer)
• Output: the following shape when n=5
5 4 3 2 1
5 4 3 2
5 4 3
5 4
5

23. Problem
• Input: n (integer)
• Output: the following shape when n=4
1
1 2 3
1 2 3 4 5
1 2 3 4 5 6 7

25. References
• https://www.programtopia.net/cprogramming/docs/
nested-loop
• Number pyramids:
http://www.codeforwin.in/2016/06/number-
pattern-programs-in-c.html
• Star pyramids:
http://www.codeforwin.in/2015/07/star-patterns-
program-in-c.html