# contains "stdio.h"
Master ()
{
int n，sum = 0；
Printf ("Please enter a four-digit natural number:");
scanf("%d "，& ampn)；
while(n & gt； = 10000 | | n & lt； 1000)
{
Printf ("Input error, please re-enter!" );
scanf("%d "，& ampn)；
}
sum = n % 10+n/ 10% 10+n/ 100% 10+n/ 1000；
Printf("\n%d, the sum of digits is: %d ",n, sum);
getch()；
}
2. Programming, converting the length value in inches into the length value in centimeters, and the output accuracy is 10-3, which requires a friendly interface.
Conversion formula: 1 inch =2.54 cm.
# contains "stdio.h"
Master ()
{
Double n;
Printf ("Please enter a length value (inches):");
scanf("%lf "，& ampn)；
while(n & lt； 0)
{
Printf ("Input error, please re-enter!" );
scanf("%lf "，& ampn)；
}
printf(" \ n % lf inch = % 10.3 lf cm "，n * 2.54+0.0005)；
getch()；
}
3. Programming, input a character and output the ASCII code of the character.
# contains "stdio.h"
Master ()
{
char n；
Printf ("Please enter a character:");
scanf("%c "，& ampn)；
Printf (ASCII value is "\ n% c is: %d", n, n);
getch()；
}
4. Write a program to convert the input Fahrenheit temperature value into Celsius temperature value, and the accuracy of the output result is 0. 1 (the conversion formula is found online on Baidu and other tools).
# contains "stdio.h"
Master ()
{
Double f, c;
Printf ("Please enter a Fahrenheit temperature value (f):");
scanf("%lf "，& ampf)；
c = 5 *(F-32)/9+0.05；
Printf("\n%lf Fahrenheit =%. 1lf Celsius ",f, c);
getch()；
}
5. Enter the values of three sides of the triangle and calculate the area of the triangle. The accuracy of the result is 10-3 (the conversion formula is found in online Baidu and other tools).
# contains "stdio.h"
# contains "math.h"
Master ()
{
Double a, b, c, s, s;
Printf ("Please enter three sides of the triangle:");
Scanf("%lf, %lf, %lf ",& one, & c)；
while(a+b & lt； = c | | a+c & lt； = b | | b+ c & lt； =a)
{
Printf ("input error, cannot form triangle, please re-enter!" );
Scanf("%lf, %lf, %lf ",& one, & c)；
}
s =(a+b+c)/2；
s = sqrt(s *(s-a)*(s-b)*(s-c))+0.0005；
Printf(" \ n The area of triangle is:% 10.3lf ",s);
getch()；
}
(additional questions) 6. Programming converts decimal numbers input by users into hexadecimal numbers and octal numbers for output, which requires a friendly interface.
# contains "stdio.h"
Master ()
{
int n；
Printf ("Please enter a decimal:");
scanf("%d "，& ampn)；
Printf("\n%d converted to octal number: %o ",n, n);
Printf("\n%d converted to hexadecimal number: %x ",n, n);
getch()；
}