C - Use Nested for Loops to draw box

Introduction

The following code outputs a box with a fixed height and width.

The first step is to define variables that specify the number of characters for the width and the height:

unsigned int width = 0;
unsigned int height = 0;

You can define a variable representing a minimum dimension value for the box:

const unsigned int MIN_SIZE = 3;        // Minimum width and height values

You could read in the width and height next:

printf("Enter values for the width and height (minimum of %u):", MIN_SIZE);
scanf("%u%u", &width, &height);

here's the complete program:

Demo

#include <stdio.h>

int main(void)
{
  const unsigned int MIN_SIZE = 3;          // Minimum width and height values
  unsigned int width = 0;
  unsigned int height = 0;

  // Read in required width and height
  printf("Enter values for the width and height (minimum of %u):", MIN_SIZE);
  scanf("%u%u", &width, &height);
  // Validate width and height values
  if (width < MIN_SIZE)
  {//from www.ja  v a 2s  .  co  m
    printf("\nWidth value of %u is too small. Setting it to %u.", width, MIN_SIZE);
    width = MIN_SIZE;
  }
  if (height < MIN_SIZE)
  {
    printf("\nHeight value of %u is too small. Setting it to %u.", height, MIN_SIZE);
    height = MIN_SIZE;
  }
  // Output the top of the box with width asterisks
  for (unsigned int i = 0; i < width; ++i)
    printf("*");

  // Output height-2 rows of width characters with * at each end and spaces inside
  for (unsigned int j = 0; j < height - 2; ++j)
  {
    printf("\n*");                               // First asterisk

                           // Next draw the spaces
    for (unsigned int i = 0; i < width - 2; ++i)
      printf(" ");

    printf("*");                                 // Last asterisk

  }
  // Output the bottom of the box
  printf("\n");                                  // Start on newline
  for (unsigned int i = 0; i < width; ++i)
    printf("*");

  printf("\n");                                  // Newline at end of last line
  return 0;
}

Result

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