3. Variables និង Arithmetic Expression

កម្មវិធីបន្ទាប់ប្រើប្រាស់រូបមន្ត Celsius=5*Fahrenheit-32/9 ដើម្បីធ្វើការបង្ហាញតារាងបំលែង Celsius ទៅ Fahrenheit ដោយ Loop ម្ដង 20 degree និងធំបំផុតត្រឹម 300 degree។

Console:

#include <stdio.h>/*Include standard library*/
/*Fahrenheit-Celsius Table*/
int main(void)/*Define function main*/
{/*start function main*/
 int celsius, fahr;/*variable celsius and fahr as integer (identifier)*/
 int lower=0, upper=300, step=20;/*variable lower, upper, step as integer*/
 printf("Fahrenheit\tCelsius\n");/*print header of table*/
 fahr = lower;/*first value of fahr is 0*/
 while (fahr<=upper)/*do loop until fahr=upper*/
 {/*start while loop*/
  celsius = 5*(fahr - 32) / 9;/*value of celsius*/
  printf("%d\t\t%d\n",fahr,celsius);/*print %d (decimal) by order fahr, celsius*/
  fahr = fahr + step;/*increase fahr by step(20)*/
 }/*end while loop*/
 return 0;/*exited function main*/
}

Output:

Fahrenheit      Celsius

0               -17

20              -6

40              4

60              15

80              26

100             37

120             48

140             60

160             71

180             82

200             93

220             104

240             115

260             126

280             137

300             148

Console:

#include <stdio.h>/*Include standard library*/
/*Fahrenheit-Celsius Table*/
int main(void)/*Define function main*/
{/*start function main*/
 float celsius, fahr;/*variable celsius and fahr as float (identifier)*/
 int lower = 0, upper = 300, step = 20;/*variable lower, upper, step as integer*/
 printf("Fahrenheit\tCelsius\n");/*print header of table*/
 fahr = lower;/*first value of fahr is 0*/
 while (fahr <= upper)/*do loop until fahr=upper*/
 {/*start while loop*/
  celsius = 5 * (fahr - 32) / 9;/*value of celsius*/
  printf("%.0f\t\t%.2f\n", fahr, celsius);/*print %f (float) by order fahr, celsius .0 or .2 or 0.2 show number after (.) */
  fahr = fahr + step;/*increase fahr by step(20)*/
 }/*end while loop*/
 return 0;/*exited function main*/
}

Output:

Fahrenheit      Celsius
0               -17.78
20              -6.67
40              4.44
60              15.56
80              26.67
100             37.78
120             48.89
140             60.00
160             71.11
180             82.22
200             93.33
220             104.44
240             115.56
260             126.67
280             137.78
300             148.89

យើងមានមួយរបៀបទៀត៖

#include <stdio.h>
int main(void)
{
 int fahr;
 printf("Fahrenheit\tCelsius\n");
 for (fahr = 0; fahr <= 300; fahr=fahr + 20)
 {
  printf("%3d\t\t%6.1f\n",fahr,(5.0/9.0)*(fahr-32));
 }
 return 0;
}

សេចក្ដីពន្យល់

int ហៅថា identifier មានប្រភេទទិន្នន័យជា Integer។
celsius, fahr, lower, upper, step ហៅថា Variable។ បានសេចក្ដីថាអ្វីដែលនៅក្រោយ identifier គឺជា variable។
lower=0, upper=300, step=20 ហៅថា initial value ឬតម្លៃដំបូង។
while(){} គឺប្រភេទ while loop មានតួនាទីធ្វើការម្ដងហើយម្ដងទៀត ដោយមានចំណុចចាប់ផ្ដើម និងបញ្ចប់ណាមួយ។
%d គឺសំដៅទៅលើការទទួលយកតម្លៃជាប្រភេទចំនួនគត់ integer។
+, -, *, /,% (remainder)... ហៅថា arithmetic expression។

ឧទាហរណ៍២៖ 
ការគណនារកផ្ទៃក្រឡា។

Console:

#include<stdio.h>/*include standard library*/
int main(void)/*define function main()*/
{/*start function main()*/
 float base, height, length, topbase, bottombase, area;/*variables declare as float number*/
 int shape;/*user's choice*/
 printf("Welcome! Area calculation!\n"); 
 printf("1. Square\n");
 printf("2. Rectangle\n");
 printf("3. Triangle\n");
 printf("4. Trapezium\n");
 printf("5. Paralllelogram\n");
 printf("6. Rhombus\n");
 printf("7. Kite\n");
 printf("Please, chose one of these (put number only):\n");
 scanf_s("%d",&shape);/*& get the address of variable shape in memory where it located*/
 
 if (shape == 1||shape==2||shape==5)/*If user input 1, 2, 5 are the same formula. || mean "or"*/
 {  
  printf("Base=");
  scanf_s("%f",&base);
  printf("Height=");
  scanf_s("%f",&height);
  area= (base * height);
  printf("Area=%f", area);
 }
 else if (shape==3)
 {
  printf("Base=");
  scanf_s("%f",&base);
  printf("Height=");
  scanf_s("%f", &height);
  area = (base * height) / 2;
  printf("Area=%f", area);
 }
 else if (shape==4)
 {
  printf("Top Base=");
  scanf_s("%f", &topbase);
  printf("Bottom Base=");
  scanf_s("%f",&bottombase);
  printf("Height=");
  scanf_s("%f",&height);
  area = ((topbase + bottombase) * height) / 2;
  printf("Area=%f", area);
 }
 else if (shape==6||shape==7)
 {
  printf("Lenght=");
  scanf_s("%f",&length);
  printf("Height=");
  scanf_s("%f", &height);
  area = (length * height) / 2;
  printf("Area=%f",area);
 }
 else
 {
  printf("Sorry! Try again!\n");/*if user input non of choice*/
 }
 return 0;
}

Output:

Welcome! Area calculation!
1. Square
2. Rectangle
3. Triangle
4. Trapezium
5. Paralllelogram
6. Rhombus
7. Kite
Please, chose one of these (put number only):
1
Base=4
Height=6
Area=24.000000

ឧទាហរណ៍៣៖ 
ការគណនាលុយខ្មែរទៅជាលុយដុល្លារសហរដ្ឋអាមេរិក និងពីដុល្លារសហរដ្ឋអាមេរិកទៅជាលុយខ្មែរវិញ។
Console:

#include <stdio.h>
int main(void)
{
 int khmer_currency, us_currency, rate,choice;
 printf("Currency Conversion\n");
 printf("--------------------\n");
 printf("1. Khmer Riel-->US Dollar\n2. US Dollar-->Khmer Riel\n");
 printf("--------------------\n");
 printf("Current Rate 1$=");
 scanf_s("%d", &rate);
 printf("Please, chose one of these:");
 scanf_s("%d",&choice);
 if (choice==1) 
 {
  printf("Khmer Riel Amount=");
  scanf_s("%d",&khmer_currency);
  us_currency = khmer_currency / rate;
  printf("US Dollar Amount=$%d",us_currency);
 }
 else if (choice==2)
 {
  printf("US Dollar Amount:");
  scanf_s("%d",&us_currency);
  khmer_currency = us_currency * rate;
  printf("Khmer Riel Amount=%dR",khmer_currency);
 }
 else
 {
  printf("Sorry! Out of choice!\n");
 }
 return 0;
}

Output:

Currency Conversion
--------------------
1. Khmer Riel-->US Dollar
2. US Dollar-->Khmer Riel
--------------------
Current Rate 1$=4000
Please, chose one of these:2
US Dollar Amount:100
Khmer Riel Amount=400000R

ឧទាហរណ៍៣៖ 
Global Variable និង Static Variable

Console:

#include <stdio.h>
int globalvar;/*Global Variable*/
int main(void)
{
 static int staticva;/*Static variable*/
 int sum;
 printf("Input Global Variable:");
 scanf_s("%d",&globalvar);
 printf("Input Static Variable:");
 scanf_s("%d",&staticva);
 sum = globalvar + staticva;
 printf("Sum is %d",sum);
}

Output:

Input Global Variable:34
Input Static Variable:21
Sum is 55