程序代码：

// printfdemo.c-- printf()函数用法示例
#include <stdio.h>

char *m1 = "Binary";
char *m2 = "Decimal";
char *m3 = "Octal";
char *m4 = "Hexadecimal";

int main(void)
{
float d1 = 10000.123;
int n;

puts("Outputting a number with different field widths.\n");
printf("%5f\n", d1);
printf("%10f\n", d1);
printf("%15f\n", d1);
printf("%20f\n", d1);
printf("%25f\n", d1);

puts("\n Press Enter to continue...");
fflush(stdin);
getchar();

puts("\nUse the * field width specifier to obtain field width");
puts("from a variable in the argument list.\n");

for (n = 5; n <= 25; n += 5)
printf("%f %*f\n", d1, n, d1);

puts("\n Press Enter to continue...");
fflush(stdin);
getchar();

puts("\nInclude leading zeros.\n");

printf("%05f\n", d1);
printf("%010f\n", d1);
printf("%015f\n", d1);
printf("%020f\n", d1);
printf("%025f\n", d1);

puts("\n Press Enter to continue...");
fflush(stdin);
getchar();

puts("\nDisplay in octal, decimal, and hexadecimal.");
puts("Use # to precede octal and hex output with 0 and 0X.");
puts("Use - to left-justify each value in its field.");
puts("First display column labels.\n");

printf("%-15s%-15s%-15s", m2, m3, m4);

for (n = 1; n < 20; n++)
printf("\n%-15d%-#15o%-#15X", n, n, n);

puts("\n Press Enter to continue...");
fflush(stdin);
getchar();

puts("\nUse the %n conversion command to count characters.\n");
printf("%s%s%s%s%n", m1, m2, m3, m4, &n);
printf("\n\nThe last printf() output %d characters .\n", n);

return 0;
}