Printing a character n time based on input

Question

I am writing a program that will print the "*" based on the users input, the user will need to enter a number between 1 and 30 an the program will print the * n time. where n is between 1 and 30.

ex: user enters 7 output is "*******" for any n value between 1 and 30.

this is what i got so far:

int x;
char c = "*";

printf("%s","Please Enter a number between 1 and 30\n");
scanf("%d", &x);

if (x>=1)
{
    printf("%d",x,c);;
}

looking for some guidance on the printf part, how do i get it to print the * by what x is, this is the lower limit as 1 is the lowest the user can enter 30 is the upper limit but usually i like to make sure the lower limit works first before the upper then its a simple copy paste and change the numbers. A separate if will be for any number out of bounds i.e anything less then 1 and greater then 30 will require the user to reenter, so far it just prints the number that was entering not the * that many times. Also if i have any other mistakes in my code feel free to correct me still learning.

Answer 1

You just need to replace your idea 'print once a group of N characters'
with 'print N times one character'.

Then the solution is straight-forward:

if (x >= 1 && x <= 30)    // test number of chars to print
{
    while (--x >= 0)      // decrement it and see if anything remains
        printf("*");      // print a character and reiterate

    printf("\n");         // terminate the output line
}
else
    printf("The value entered is not between 1 and 30.\n");   // error message

EDIT

Based on the answer by @RobertS supports Monica Cellio, you can make special use of the requirement that the output shall be a simple string of repeated single character, and that the size of the output is strictly limited to quite small length.

So you can define an explicit array of characters, containing the longest possible output string required:

const char outString[31] = "******************************";

The length of 31 suffices for 30 asterisks '*' and a zero character (ASCII NUL code), terminating the string.

When you want to output a string containing x asterisks, you can print a tail part of the string, starting at appropriate position:

if (x >= 1 && x <= 30)         // test number of chars to print
    puts( outString + 30 - x); // print appropriate part of the string
else
    puts("The value entered is not between 1 and 30.");

This way you avoid both the printf formatting and a loop overhead – at the cost of declaring a constant array.

Answer 2

One way is using a loop and print one * at each iteration:

unsigned int x;

printf("Please Enter a number between 1 and 30\n");
if (scanf("%u", &x) != 1)
{
    // error routine.
}

if (x >= 1 && x <= 30)
{
    while (x--)
    {
        printf("%c", '*');
    }

    puts("");
}
else
{
    printf("Wrong input value!\n");
}

---

If you want to print the sequence of *s by just one printf() call,

One way is using a string literal of 30 *s and only display the amount of *s the user entered. The printing is possible with the .* modifier which provides the length of the output string relative to the value of the given argument x.

unsigned int x;
const char* p = "******************************";

printf("Please Enter a number between 1 and 30\n");
if (scanf("%u", &x) != 1)
{
    // error routine.
}

if (x >= 1 && x <= 30)
{
    printf("%.*s\n", x, p);
}
else
{
    printf("Wrong input value!\n");
}

A few notes here:

• You need to change if (x >= 1) to if (x >= 1 && x <= 30) because it only should print the value if the values between 1 and 30 not only if 1 or above.

• Always check the return of input functions such as scanf() if an error occurred.

• I changed the type of x to unsigned int because its clear that it shouldn't have a negative value. Take care of that you need to change the format specifier in scanf() from %d to %u.

Answer 3

This initialization of an object of the type char

char c = "*";

is wrong. Instead of the string literal "*" you have to use the character literal '*' like

char c = '*';

This call of printf

printf("%s","Please Enter a number between 1 and 30\n");

is too complicated. You could just write

printf("Please Enter a number between 1 and 30\n");

And this call of printf with a redundant null-statement

printf("%d",x,c);;

has an unused argument and does not do what you think it should do.

Moreover this if statement

if (x>=1)

does not check whether x is less than or equal to 30.

Beside this the user can interrupt the input. In this case the variable x will have indeterminate value if it is declared with automatic storage duration that is within a block.

Try never to use magic numbers as 1 or 30. Instead use named constants.

As the number of the repeated output characters can not be negative declare the corresponding variable x as having an unsigned integer type.

Here is a demonstrative program that shows how the code can be written.

#include <stdio.h>

int main(void) 
{
    const unsigned int MIN_VALUE = 1;
    const unsigned int MAX_VALUE = 30;
    const char c = '*';
    
    printf( "Please Enter a number between %u and %u inclusive: ", 
            MIN_VALUE, MAX_VALUE );
            
    unsigned int n;
    
    if ( scanf( "%u", &n ) == 1 && MIN_VALUE <= n && n <= MAX_VALUE )
    {
        putchar( '\n' );
        
        do
        {
            putchar( c );
        } while ( n-- != MIN_VALUE );
        putchar( '\n' );
    }
    else
    {
        puts( "\nSorry. The input is not valid." );
    }
    
    return 0;
}

The program output might look like

Please Enter a number between 1 and 30 inclusive: 20

********************

Answer 4

//enter a numbers between 1 and 30 and print the character as per the entered number 

#include<stdio.h>

void main()
{

    int n;
    printf("Enter a number between 1 and 30 only  :\n ");
    scanf("%d",&n);
    if(n>=1 && n<=30)
    {
        for(int i=1; i<=n; i++)
        {
            printf("*");
        }
    }
    else
    {
         printf("Please enter a number only between 1 and 30");
    }
}

Answer 5

For this purpose the most effizient was is to use fwrite. Other than for example printf, you have to tell the function how many character to write.

printf("%s","Please Enter a number between 1 and 30\n");
scanf("%d", &x);

if (x >= 1 && x <= 30) {
    char outbuffer[30];
    memset(outbuffer, '*', 30); // fill outbuffer with '*'
    fwrite(outbuffer, 1, x, stdout);
}
else ...

The fwrite function takes 4 arguments. The first argument is a pointer to bytes you want to write. Ignore the second. The third argument is the amount of elements you want to write and finally the fourth is where you wamt to write it to. stdout is the standart output.

An other way to do it, that escentially does the same, is to use a loop and putchar.

printf("%s","Please Enter a number between 1 and 30\n");
scanf("%d", &x);

if (x >= 1 && x <= 30) {
    for (int i = 0; i < x; i++) {
        putchar('*');
    }
}
else ...

For loops are seperated by ; into 3 pieces. The first int i = 0 will be run at the start and creates an integer called i and sets it to 0. The second is the condition. The loop runs as long as the condition is true or not 0. The last part is executed at the end of every loop iteration.

for (foo(); bar(); buzz()) {/* */}

Is the same as

foo();
while (bar()) {
    /* */
    buzz();
}