The document discusses control flow in C programming. It covers various control flow statements like if-else, switch case, loops etc. Key points include: - Control flow specifies the order of computations. Statements are terminated with semicolons. Blocks of statements are grouped with curly braces. - if-else and nested if statements execute code based on expression evaluations. if-else if provides multi-way decisions. - switch-case provides a way to select one choice from many cases based on a variable's value. - Loops like for, while, do-while repeat a block of code. - The goto statement changes execution flow without checking conditions. -

1. Control Flow in C

2. Control Flow
The control-flow of a language specify the order in which
computations are performed.
Statements: An expression such as x = 0 or i++ or printf(...)
becomes a statement when it is followed by a semicolon, as in
x = 0;
i++;
printf(...);
In C, the semicolon is a statement terminator, rather than a separator
Blocks or Statement Blocks: In C, any sequence of statement
can be grouped together by enclosing pair of curly braces.
Inside statement block variable declaration is allowed.
There is no semicolon after the right brace that ends a block.
2

3. Statement Blocks (cont..)
Statement block introduces a new scope in the program.
A scope is part of the program within which a variable remains
defined.
Every function has a function body consisting of s set of one or more
statements, i.e. a statement block, due to this reason , every function
body is confined within a pair of curly braces.
3
Program-1
#include<stdio.h>
main(){
int a=3;
{
int a=10;
printf(“a=%d",a);
}
printf(“na=%d",a);
}
Program-2
#include<stdio.h>
main(){
int a=3;
{
int b=10;
printf(“a=%d",a);
}
printf(“nb=%d",b);
}
a=10
a=3

4. What will be the output ?
main()
{
int x=40;
{
int x=20;
printf(“x=%d",x);
}
printf(“nx=%d",x);
}
4
x=20
x=40

5. Flow control Statements
Following are some constructs for controlling the flow of
execution in C:
1. if,
2. if – else,
3. Nested if and
4. if – else if
5. switch
6. conditional operator
7. goto
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6. IF Statements
Syntax:
if(expression)
statement
• The expression is evaluated; if it is true (that is, if expression has a
non-zero value), statementis executed.
• Note: here statement may be single statement or Statement
Block.Just like
if(expression)
{
stmt 1;
stmt 2;
………..
}
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7. IF Statements Example
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8. IF Statements Example
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9. Since an if tests the numeric value of an expression, certain
coding shortcuts are possible. The most obvious is writing
if (expression) instead of if (expression != 0)
in last example if(a%2!=0) can be written as if(a%2)
Following three statements are functionally equevalent
if(x)
if(x!=0)
if(!(x==0))
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10. IF - ElSE Statements
if (expression)
statement1
else
statement2
 The expression is evaluated; if it is true (that is, if expression has
a non-zero value), statement1is executed. If it is false (expression
is zero) statement2is executed.
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11. IF - ElSE Statements
if (n > 0)
if (a > b)
z = a;
else
z = b;
the else goes to the inner if, as we have shown by indentation. If that isn't what you
want, braces must be used to force the proper association:
if (n > 0) {
if (a > b)
z = a;
}
else
z = b;
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12. if - else Example
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13. if - else Example
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14. NESTED IF Statements
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15. NESTED IF Example
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16. IF – ELSE IF Statements
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17. IF – ELSE IF Statements
This sequence of if statements is the most general way of
writing a multi-way decision.
The expressions are evaluated in order; if an expression is
true, the statement associated with it is executed, and this
terminates the whole chain.
The last else part handles the “none of the above'' or default
case where none of the other conditions is satisfied.
Sometimes there is no explicit action for the default; in that
case the trailing
else can be omitted, or it may be used for error checking to
catch an ``impossible'' condition.
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18. IF – ELSE IF Example
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19. IF – ELSE IF Example
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20. IF – ELSE IF Example
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21. Switch Statements
Switch is used to Select one choice (case) from many cases.
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22. Switch-Case Example1
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23. Switch-Case Example2
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24. Switch-Case Related Rules
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25. Switch-Case Related Rules
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26. Example3
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27. What would be the o/p of the following program?
27
main()
{
int i=4;
switch(i)
{
default:
printf(“n a mouse”);
break;
case 1:
printf(“n a rabbit”);
break;
case 2:
printf(“n a tiger”);
break;
case 3:
printf(“n a lion”);
}
}
a mouse
08/23/15

28. Switch example
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switch (choice = getchar())
{
case ‘r’ :
case ‘R’: printf(“Red”);
break;
case ‘b’ :
case ‘B’ : printf(“Blue”);
break;
case ‘g’ :
case ‘G’:
printf(“Green”);
break;
default:
printf(“Black”);
}

29. What would be the o/p of the following program?
29
main()
{
int x=1;
switch(x)
{
printf(“Hello”);
case 1:
printf(“n JUET”);
break;
case 2;
printf(“n Good”);
break;
}
}
Explanation: Though there is no error ,the first printf statement can never be
executed irrespective of the value of x . In other words all the statements in the
switch have to belong to some case or other.
JUET
08/23/15

30. What will be the output?
Q1:
main()
{
printf(“%d, %d, %d”,sizeof(3.14f),sizeof(3.14),sizeof(3.14l));
}
Q2:
main()
{
int a=010;
printf(“a=%d”,a);
}
Q3:main(){
float c=3.14;
printf(“%f”,c%2);
} 08/23/1530
4, 8, 10
a=8 // printf(“a=%o”); would print a=10
Similarly printf(“a=%x”); would print a=8( equivalent hex)
Error:Illigal use of floating poit in function main

31. What will be the output?
Q1:
main()
{int a=5;
a=printf(“Hello”) +printf(“JUET”);
printf(“%d”,a);
}
Q2:main(){
printf(“Hi”);
if(!-1)
printf(“Bye”);
}
Q3:main(){ int a=40000,b=20000;
if(a<b)
printf(“Wow!”);
else printf(“Really!”);
}
08/23/1531
o/p: HelloJUET9
o/p: Hi
o/p: Wow! //Because of integer overflow a
will have 40000-65536=-25536

32. The Conditional Operator ?:(Ternary
operator)
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33. Conditional Operator Example-1
void main()
{
int a;
printf(“Enter a no.”);
scanf(“%d”,&a);
a%2==0?printf(“No. is even”):printf(“No. is odd”);
}
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34. Conditional Operator Example-2
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35. What will be the output?
main()
{
int a=10,b;
a>=5?b=100:b=200;
printf(“%d”,b);
}
08/23/1535
o/p: 100

36. Goto Statements
Goto changes the flow of execution without checking any
condition
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37. Use of Goto Statements
Nevertheless, there are a few situations where gotos may find a place.
The most common use is to abandon processing in some deeply nested
structure, such as breaking out of two or more loops at once.
The break statement cannot be used directly since it only exits from
the innermost loop. Thus:
for ( ... )
for ( ... ) {
...
if (disaster)
goto error;
}
...
error: // goto will transfer the control to this statement.
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38. Some facts about goto
A label has the same form as a variable name, and is followed
by a colon.
It can be attached to any statement in the same function as
the goto.
The scope of a label is the entire function.
With a few exceptions like previous example, code that uses
goto statements is generally harder to understand and its very
difficult to maintain as compare to the code without gotos.
Due to above reason goto is rarely used in programming.
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39. Some Tips
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40. What will be the Output
Q1#include<stdio.h>
main(){
int a=10,b=50;
if(a>b);
printf("a is greater than bn");
printf("End of program");
}
Q2:
main(){
int a=55,b=10;
if(a>b)
printf("a is greater than bn");
printf("Very Good!");
else printf("a is smaller than b");
}
08/23/1540
o/p: a is greater than b
End of program
o/p: Error: Misplaced else in function main

41. What will be the Output
Q3#include<stdio.h>
main(){
float F;
F=20000*3/3.0;
printf(“F=%f“,F);
}
Q4:
main(){
int a=20,b=10;
b=2a;
printf(“a=%dn“,a);
printf(“b=%d“,b);
}
08/23/1541
o/p: F=-1845.333374
o/p:Compilation Error