C Program to Print Numbers 1 to n

You can print numbers from 1 to n in C using a for loop like this: for(int i = 1; i <= n; i++) printf("%d\n", i); inside your main function.

Examples

Input1

Output1

Input5

Output1 2 3 4 5

Input0

Output

How to Think About It

To print numbers from 1 to n, start counting from 1 and keep increasing the count by 1 until you reach n. For each number, print it on the screen. If n is zero or less, print nothing.

Algorithm

1

Get input number n from the user

2

Start a counter i at 1

3

While i is less than or equal to n, do the following:

4

Print the current value of i

5

Increase i by 1

6

Stop when i becomes greater than n

Code

c

#include <stdio.h>

int main() {
    int n, i;
    scanf("%d", &n);
    for(i = 1; i <= n; i++) {
        printf("%d\n", i);
    }
    return 0;
}

Output

1
2
3
4
5

Dry Run

Let's trace the program with input n = 5 through the code

1

Input

User enters n = 5

2

Initialize counter

Set i = 1

3

Check condition

Is i (1) <= n (5)? Yes, continue

4

Print number

Print 1

5

Increment counter

i becomes 2

6

Repeat loop

Check if i (2) <= 5, print 2, increment i to 3, and so on until i = 6

7

End loop

When i = 6, condition i <= 5 is false, stop loop

i	Condition i <= n	Action
1	true	Print 1, i++ to 2
2	true	Print 2, i++ to 3
3	true	Print 3, i++ to 4
4	true	Print 4, i++ to 5
5	true	Print 5, i++ to 6
6	false	Exit loop

Why This Works

Step 1: Reading input

The program reads the number n from the user using scanf to know how many numbers to print.

Step 2: Looping from 1 to n

The for loop starts at 1 and runs until it reaches n, printing each number in order.

Step 3: Printing numbers

Inside the loop, printf outputs the current number followed by a new line, so each number appears on its own line.

Alternative Approaches

while loop

c

#include <stdio.h>

int main() {
    int n, i = 1;
    scanf("%d", &n);
    while(i <= n) {
        printf("%d\n", i);
        i++;
    }
    return 0;
}

Uses a while loop instead of for; functionally the same but some find it clearer for beginners.

do-while loop

c

#include <stdio.h>

int main() {
    int n, i = 1;
    scanf("%d", &n);
    if(n > 0) {
        do {
            printf("%d\n", i);
            i++;
        } while(i <= n);
    }
    return 0;
}

Uses do-while to ensure at least one print if n > 0; requires an if check to avoid printing when n <= 0.

Complexity: O(n) time, O(1) space

Time Complexity

The loop runs from 1 to n, so it executes n times, making the time complexity O(n).

Space Complexity

The program uses a fixed number of variables and prints output directly, so space complexity is O(1).

Which Approach is Fastest?

All loop methods (for, while, do-while) have the same time and space complexity; choice depends on readability and style.

Approach	Time	Space	Best For
for loop	O(n)	O(1)	Simple counting with known range
while loop	O(n)	O(1)	When condition checked before each iteration
do-while loop	O(n)	O(1)	When at least one iteration is needed