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1. Chapter 3
C Language Control
Mr.Warawut Khangkhan
Twitter: http://twitter.com/awarawut
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E-Mail: awarawut@hotmail.com
Mobile: 083-0698-410

2. Contents
Decision / Selection
Loop / Repetition
Break and Continue Statement
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3. DECISION / SELECTION
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4. Decision / Selection
if then
if then else
Nested if
switch
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5. if then
Format:
if (expression)
statement;
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6. if then
Format:
if (expression) {
statement-1;
statement-2;
…
}
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7. Example if1.c
#include <stdio.h>
#include <stdlib.h>
int main( ) {
int i;
scanf(“%d”, &i);
if (i > 0)
printf(“a positive number was enteredn”);
system(“PAUSE”);
return 0;
}
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8. Example if2.c
#include <stdio.h>
#include <stdlib.h>
int main( ) {
int i;
scanf(“%d”, &i);
if (i < 0) {
printf(“a negative number was enteredn”);
i = -i;
}
system(“PAUSE”);
return 0;
} Mr.Warawut Khangkhan Chapter 3 C Language Control 8

9. if then else
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10. if then else
Format:
if (expression)
statement-true;
else
statement-false;
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11. if then else
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12. if then else
Format:
if (expression) {
statement-1;
statement-2;
…
} else {
statement-3;
statement-4;
…
}
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13. Example ifthen1.c
#include <stdio.h>
#include <stdlib.h>
int main( ) {
int i;
scanf(“%d”, &i);
if (i > 0)
printf(“a negative number was enteredn”);
else
printf(“a negative number was enteredn”);
system(“PAUSE”);
return 0;
} Mr.Warawut Khangkhan Chapter 3 C Language Control 13

14. Nested if
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15. Nested if
Format:
if (expression-1)
statement-1;
else if (expression-2)
statement-2;
else if (expression-3)
statement-3;
else
statement-4;
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16. Example nestedif.c
#include <stdio.h>
#include <stdlib.h>
int main( ) {
int score;
printf(“Enter score : “);
scanf(“%d”, &score);
if (score > 79)
printf(“Very Goodn”);
else if (score > 49)
printf(“Goodn”);
else
printf(“Badn”);
}
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17. switch
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18. switch
Format:
switch (expression) {
case const-expr.1: statement-1; break;
case const-expr.2: statement-2; break;
case const-expr.3: statement-3; break;
…
[default: statement-default;]
}
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19. Example switch1.c
#include <stdio.h>
#include <stdlib.h>
int main( ) {
char ch;
printf(“Enter char : “);
ch = getchar( );
switch (ch) {
case 'a': case 'A': printf(“Additionn”); break;
case 's': case 'S': printf(“Subtractn”); break;
case 'q': case 'Q': printf(“Quitn”); break;
default: printf(“Other Charactern”);
}
system(“PAUSE”);
return 0;
} Mr.Warawut Khangkhan Chapter 3 C Language Control 19

20. Example switch2.c
#include <stdio.h>
#include <stdlib.h>
int main( ) {
int n = ?;
swicth (n) {
case 2: n++;
case 4: n++; break;
case 6: n++; break;
case 8: n++;
default: n++;
}
printf(“N = %dn”, n);
system(“PAUSE”);
return 0;
} Mr.Warawut Khangkhan Chapter 3 C Language Control 20

21. LOOP / REPETITION
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22. Loop / Repetition
while loop
do ... while loop
for loop
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23. while loop
Format:
while (expression)
statement;
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24. while loop
Format:
while (expression) {
statement-1;
statement-2;
…
}
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25. Example while1.c
#include <stdio.h> while (num <= 10) {
#include <stdlib.h> printf(“%dn”, num);
num++;
int main( ) { }
int num = 1;
while (num <= 10)
printf(“%dn”, num++);
system(“PAUSE”);
return 0;
}
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26. Example while2.c
#include <stdio.h>
#include <stdlib.h>
int main( ) {
int num = 1;
int sum = 0;
while (num <= 10) {
sum += num; // sum = sum + num;
num++; // num = num + 1;
}
printf(“Summary of 1-10 = %dn”, sum);
system(“PAUSE”);
return 0;
} Mr.Warawut Khangkhan Chapter 3 C Language Control 26

27. do ... while loop
Format:
do
statement;
while (expression);
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28. do ... while loop
Format:
do {
statement-1;
statement-2;
…
} while (expression);
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29. Example dowhile1.c
#include <stdio.h> do {
#include <stdlib.h> printf(“%dn”, num);
int main( ) { num++;
int num = 1; } while (num <= 10);
do
printf(“%dn”, num++);
while (num <= 10);
system(“PAUSE”);
return 0;
}
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30. Example dowhile2.c
#include <stdio.h>
#include <stdlib.h>
int main( ) {
int num = 1;
int sum = 0;
do {
sum += num; // sum = sum + num;
num++; // num = num + 1;
} while (num <= 10);
printf(“Summary of 1-10 = %dn”, sum);
system(“PAUSE”);
return 0;
} Mr.Warawut Khangkhan Chapter 3 C Language Control 30

31. for loop
Format:
for (expr.1; expr.2; expr.3)
statement;
or
for (expr.1; expr.2; expr.3) {
statement-1;
statement-2;
…
}
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32. Example for1.c
#include <stdio.h> for (num = 1; num <= 10; ) {
#include <stdlib.h> printf(“%dn”, num);
num++;
int main( ) { }
int num;
for (num = 1; num <= 10; num++)
printf(“%dn”, num);
system(“PAUSE”);
return 0;
}
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33. Example for2.c
#include <stdio.h>
#include <stdlib.h>
int main( ) {
int num = 1;
for ( ; num <= 10; ) {
printf(“%dn”, num;
num++;
}
system(“PAUSE”);
return 0;
}
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34. Example for3.c
#include <stdio.h>
#include <stdlib.h>
int main( ) {
int num;
int sum = 0;
for (num = 1; num <= 10; num++) {
sum += num; // sum = sum + num;
}
printf(“Summary of 1-10 = %dn”, sum);
system(“PAUSE”);
return 0;
}
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35. Change with for loop to while loop
for (expr.1; expr.2; expr.3)
statement;
1 2
expr.1; 4
3
while (expr.2) {
statement;
expr.3;
}
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36. Change with for loop to do .. while
loop
for (expr.1; expr.2; expr.3)
statement;
1 2
expr.1; 4
3
do {
statement;
expr.3;
} while (expr.2);
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37. Change with while loop to
do .. while loop
expr.1;
while (expr.2) { 1
statement; 2
expr.3;
}
3 expr.1;
do {
4
statement;
expr.3;
} while (expr.2);
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38. BREAK AND CONTINUE
STATEMENT
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39. Break and Continue Statement
break statement
FF F
F
continue statement
F F while, do..while for F
F
F
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40. Example break.c
#include <stdio.h>
#include <stdlib.h>
int main( ) {
int num;
for (num = 1; num <= 10; num++)
if (num == 5)
break;
else
printf(“%d”, num);
system(“PAUSE”);
return 0;
}
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41. Example continue.c
#include <stdio.h>
#include <stdlib.h>
int main( ) {
int num;
for (num = 1; num <= 10; num++)
if (num == 5)
continue;
else
printf(“%d”, num);
system(“PAUSE”);
return 0;
}
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