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CS 1001 Programming in CLecture 4
More on Decision
Making and Loops inC
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Logic Operators in if
Equal to if (x==10)
Not equal to if (x!=10) Less than if (x10)
Less than / equal to if (x=10)
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Compound Operators
Logical AND if (x==1 && y==2)
Logical OR if (x==1 || y==2)
Logical NOT if (!x)
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Single and Compound Statements
Single statements:
if (condition)
true_statement;
elsefalse_statement;
Multiple statements:
if (condition) {
}
else {
}
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Nested If Statements
void main(void)
{int winner =3;
printf(and the winner of ICC is );
if (winner==1) printf(Pakistan);
else if (winner==2)
printf(England);
else if (winner==3)
printf(WI);
else
printf(Australia);
}
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Conditional Statement
void main(void)
{
int num;
printf("Enter a value:");
scanf("%d", &num);
if (num < 0)
printf("The value is negative\n");
else if (num == 0)
printf("The value is zero\n");
else
printf("The value is positive\n");
return 0;
}
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Switch Statements
Switch statements look like thisexample:
switch (expression) {
value_1 : statements_1; break;
value_2 : statements_2; break;
...
value_n : statements_n; break
default
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switch (winner) {
case 1 : printf(Pakistan);
break;
case 2 : printf(England);
break;
.
value_n : statements_n; break
default:
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Loops
Repeat a series of statements Not reasonable to copy statements
multiple time
Need a way to repeat a block of code
Loops allow repetition
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The For Loop
Syntax: for (initialization;test;increment)
{
statements;
}
The for loop will first perform the initialization.Then, as long test is TRUE, it will execute
statements. After each execution, it willincrement.
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For loop
Known number of iterations
for(count=1;count
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For loop examples
for (x=20 ; x = 20; x -=10) from 80 to 20 in steps of -10
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While loop
Unknown number of iterations
degree =0;
while (degrees
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The While Loop
An example while loop looks like this:
void main(void)
{
char ch;
while (ch != Q || ch != q)
{
ch = getchar( );
}
}
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The Do-while Loop
The do-while loop repeatedly executes ablock of code indicated by statements aslong as the conditional expressioncond_expr is true.
do {
statements;
} while (cond_expr);
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A while for for
i=0;while(i
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A for for while
for(; degree
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Special Cases
You can have as many controlvariables as you want in loops. Thefollowing is fine:
for (x=0, y=0; x+y
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A forever loop
Using forfor(;;)
{
printf(Would you please stop teaching C\n);
}
Using while
while(1)
{printf(Would you please stop teaching C\n);
}
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Fahrenheit-to-Celsius conversionvoid main(void)
{int deg_c, deg_f;
deg_c = 0;
while (deg_c
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int main()
{
int count = 1;
while (count
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Continue & Break
The continue statement is used to forceprogram execution to the bottom of the loop,skipping any statements that come after it.
The breakstatement is used to haltexecution of a loop prior to the loops normaltest condition being met.
The exit statement causes the wholeprogram to terminate if it is called within themain program block.
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Coding for readability
int main()
{
int i,x,y;float z;
.
.
if (x < 7)
{
y= 3;
z= 4.2;}
else if (x > 23)
{
y= 5;
z= 7.2
}
for (i= 1; i < 200; i++) {
for (j= 1; j < 200; j++ {
/* Inside both loops */
}
/* Inside only the first loop */
}
return 0;}
Right bracket
level with
statement whichstarted it
Always indent after
a left bracket
Start a
left bracket aftera statement