Smiling face will be printed 5000 times. There is no logic to printing it 5000 times. It’s just a random number we selected which prints a lot of smiling faces on to the console window.
Source Code: C Program To Fill Screen With Smiling Face: Nested For Loop
Above code will print smiling faces 43 x 79 times. I just tested some random number of rows and columns and came up with these numbers. Your console window might have different number of rows and columns.
Logic To Find Prime Number Between Range, using For Loop
We ask the user to enter start and end value. We check if the value of variable start is greater than variable end. If true, we swap the values of variable start and end.
Outer For Loop Logic
We assign value of start to num and keep iterating the for loop until num is less than or equal to value of variable end. For each iteration of outer for loop num will increment by 1, from start to end value.
Inner For loop Logic
All the numbers are perfectly divisible by number 1, so we initialize the variable count to 2, instead of 1. So our inner for loop starts checking for divisibility from number 2.
The selected number(selected by outer for loop and stored in variable num), is divided by numbers 2 to num-1 times. If num is perfectly divisible by any number between 2 to num-1, then the number is not a prime number, else its a prime number.
Source Code: C Program To Find Prime Numbers Between Range, using For Loop
#include
#include
int main()
{
int start, end, num, count, prime, temp, inum;
printf("Enter start and end value\n");
scanf("%d%d", &start, &end);
if(start > end)
{
temp = start;
start= end;
end = temp;
}
printf("Prime Numbers between %d and %d are\n", start, end);
for(num = start; num
Output 1:
Enter start and end value
10
20
Prime Numbers between 10 and 20 are
11, 13, 17, 19,
Output 2:
Enter start and end value
20
10
Prime Numbers between 10 and 20 are
11, 13, 17, 19,
Output 3:
Enter start and end value
25
60
Prime Numbers between 25 and 60 are
29, 31, 37, 41, 43, 47, 53, 59,
Output 4:
Enter start and end value
50
150
Prime Numbers between 50 and 150 are
53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 127, 131, 137, 139, 149,
Output 5:
Enter start and end value
5
41
Prime Numbers between 5 and 41 are
5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41,
Logic To Find Prime Number, using For Loop
In this method, we apply square root to the selected number and store it inside variable inum. This reduces the number of iterations of inner while loop.
For example,
If num = 41;
inum = sqrt(num);
inum = sqrt(41);
inum = 6;
User entered number 41 is not perfectly divisible by any number between 2 to 6, so number 41 is a prime number.
So its enough if we iterate through the while loop sqrt(num) times to check if the selected number is divisible by any number other than 1 and itself.
Table of all prime numbers up to 1,000:
Note: We are not using curly braces around if statement because we only have 1 line of code after if – so curly braces are optional. If we have multiple lines of code, then we must use curly braces to wrap around the block of code.
Outer for loop selects number one by one for each iteration. We initialize num to 2 and for each iteration num value increments by 1. Outer for loop executes until num is less than or equal to user entered limit times.
Inner For loop Logic
All the numbers are perfectly divisible by number 1, so we initialize the variable count to 2, instead of 1. So our inner for loop starts checking for divisibility from number 2.
The selected number(selected by outer for loop and stored in variable num), is divided by numbers 2 to num-1 times. If num is perfectly divisible by any number between 2 to num-1, then the number is not a prime number, else its a prime number.
Source Code: C Program To Find Prime Numbers From 2 To N, using For Loop
#include
#include
int main()
{
int num, count, limit, prime, inum;
printf("Enter the limit\n");
scanf("%d", &limit);
printf("Prime Numbers from 2 To %d are\n", limit);
for(num = 2; num
Output 1:
Enter the limit
25
Prime Numbers from 2 To 25 are
2
3
5
7
11
13
17
19
23
Output 2:
Enter the limit
41
Prime Numbers from 2 To 41 are
2
3
5
7
11
13
17
19
23
29
31
37
41
Note: We are not using curly braces around if statement because we only have 1 line of code after if – so curly braces are optional. If we have multiple lines of code, then we must use curly braces to wrap around the block of code.
Outer for loop selects number one by one for each iteration. We initialize num to 1 and for each iteration num value increments by 1. Outer for loop executes until num is less than or equal to 300.
Inner For loop Logic
All the numbers are perfectly divisible by number 1, so we initialize the variable i to 2, instead of 1. So our inner for loop starts checking for divisibility from number 2.
The selected number(selected by outer for loop and stored in variable num), is divided by numbers 2 to num-1 times. If num is perfectly divisible by any number between 2 to num-1, then the number is not a prime number, else its a prime number.
Source Code: C Program To Find Prime Numbers From 1 To 300 using For Loop
#include
#include
int main()
{
int num, count, i, prime;
printf("Prime Numbers from 1 To 300 are\n");
for(num = 1; num
Output:
Prime Numbers from 1 To 300 are
Number 1 is neither prime nor composite
2
3
5
7
11
13
17
19
23
29
31
37
41
43
47
53
59
61
67
71
73
79
83
89
97
101
103
107
109
113
127
131
137
139
149
151
157
163
167
173
179
181
191
193
197
199
211
223
227
229
233
239
241
251
257
263
269
271
277
281
283
293
In this video tutorial we’re illustrating 3 methods to find if the user entered number is prime number or not.
For loop Logic
All the numbers are perfectly divisible by number 1, so we initialize the variable count to 2. So our c program starts checking for divisibility from number 2.
Video Tutorial: C Program To Find Prime Number or Not using For Loop
#include
int main()
{
int num, count, prime = 1;
printf("Enter a positive number\n");
scanf("%d", &num);
for(count = 2; count
Output 1:
Enter a number
7
7 is prime number
Output 2:
Enter a number
10
10 is not prime number
Logic: Method 1
We ask the user to enter a positive number and store it in variable num. Using for loop we start dividing the user entered number from 2 to num-1 times. If any number from 2 to num-1 perfectly divide the user entered number, then it’s not a prime number. We assign value 0 to variable prime and break out of the loop and print the message to the user.
Method 2 Source Code: Prime Number or Not: Divide By 2
#include
int main()
{
int num, count, prime = 1, inum;
printf("Enter a positive number\n");
scanf("%d", &num);
inum = num / 2;
for(count = 2; count
Output 1:
Enter a number
41
41 is prime number
Output 2:
Enter a number
15
15 is not prime number
Logic: Method 2
Please read the logic for method 1 above before proceeding.
In this method, we divide the user entered number by 2. This reduces the number of iterations of for loop.
If num = 41;
inum = num / 2;
inum = 41 / 2;
inum = 20;
So its enough if we iterate through the for loop 19(num/2) times to check if number 41 is perfectly divisible by any number from 2 to 20.
Method 3 Source Code: Prime Number or Not: square root Method
#include
#include
int main()
{
int num, count, prime = 1, inum;
printf("Enter a positive number\n");
scanf("%d", &num);
inum = sqrt(num);
for(count = 2; count
Output 1:
Enter a number
50
50 is not prime number
Output 2:
Enter a number
53
53 is prime number
Logic: Method 3
Please read the logic for method 1 above before proceeding.
In this method, we apply square root to the user entered number and store it inside variable inum. This reduces the number of iterations of for loop even further.
If num = 41;
inum = sqrt(num);
inum = sqrt(41);
inum = 6;
So its enough if we iterate through the while loop 5( sqrt(num) ) times to check if number 41 is perfectly divisible by any number from 2 to 6.
Table of all prime numbers up to 1,000:
Note: We are not using curly braces around if and else because we only have 1 line of code after if and else – so curly braces are optional. If we have multiple lines of code, then we must use curly braces to wrap around the block of code.
