C Language Lecture 17

Computing Fundamentals
Dr. Muhammad Yousaf Hamza
Deputy Chief Engineer, PIEAS

// Addition of two integers using
//Function
#include<stdio.h>
int addnumbers(int x, int y);
int main()
{
int num1, num2, add_result;
printf("Enter first numbern");
scanf("%d", &num1);
printf("Enter second numbern");
scanf("%d", &num2);
add_result = addnumbers(num1,
num2);
printf("Addition result is
%dn",add_result);
getchar(); return 0;
}
int addnumbers(int x, int y)
{
int z;
z = x +y;
return z;
}
Dr. Yousaf, PIEAS

// Addition of two integers using
//Function
#include<stdio.h>
int main()
{
scanf("%d", &num1);
scanf("%d", &num2);
add_result = addnumbers(num1,
num2);
%dn",add_result);
printf(“%d”, z) // Error
getchar(); return 0; }
{
int z;
z = x +y;
printf(“%d”, num1) // Error
return z;
}
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Any variable declared in a function is
not visible inside main and vice versa.

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Example of Function
// To determine the even or odd using
// a function
#include<stdio.h>
void EvenOrOdd(int num);
int main()
{
int num;
printf("Enter a number to know even
or oddn");
printf("Enter -100 to exitn");
while (1)
{
scanf("%d", &num);
if (num == -100)
break;
EvenOrOdd(num);
}
printf("OK");
void EvenOrOdd(int num)
{
if(num%2==0)
printf("Evenn");
else
printf("Oddn");
}

Dr. Yousaf, PIEAS
Example of Function
#include<stdio.h>
void printLine(void)
{
printf("n*****************n");
}
void main ()
{
int num;
printLine();
printf("Enter a Number :");
scanf("%d",&num);
if(num%2==0)
printf("Even Number");
else
printf("Odd Number");
printLine();
getchar();
}
Output
*****************
Enter a Number :13
Odd Number
*****************

Returning a value using if else statement
A single value is returned, however, multiple
return statements can be used within a single
function using “if-then-else” statement.
Dr. Yousaf, PIEAS

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// Returning a value and if else
#include<stdio.h>
int myfunc(int x, int y);
int main()
{
int num1, num2, smaller;
scanf("%d", &num1);
scanf("%d", &num2);
smaller = myfunc(num1, num2);
printf("%d is smallern",smaller);
getchar();
getchar();
return 0;
}
int myfunc(int x, int y)
{
if(x < y )
return x;
else
return y;
}

Home/Lab Assignments
Write a function that returns the greater of the two numbers i.e.
make a function that takes two integer arguments and returns the
greater of the two. Write program to use this function.
(Try Yourself)
Write a function should accept two arguments i.e. length and
width of the rectangle and should return the area of the
rectangle, the prototype of the function is as under:
float areaRect(float, float);
(Try Yourself)
Develop a function that accepts two values as length and width of
a shape and returns 0 or 1. A 1 will be returned if the shape is a
square otherwise a 0 will be returned.
(Try Yourself).
Dr. Yousaf, PIEAS

Home/Lab Assignments
A normal dice has 6 sides numbered from 1 to 6, when the dice is
rolled the number on top side of the dice is considered to be the
result of rolling the dice. Dices are used in many games etc. Your
task is to write a function int rollDice(), the function should return
an integer value ranging from 1 to 6, to make function return a
random number each time use the library function rand() and
srand() (. Write a program that allow the user to call this function
multiple times , display the value returned by the function.
(Try Yourself)
Dr. Yousaf, PIEAS

Pass by Value Versus Pass by Reference
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// Addition of two integers using Function
#include<stdio.h>
int main()
{
scanf("%d", &num1);
scanf("%d", &num2);
add_result = addnumbers(num1, num2);
%dn",add_result);
{
int z;
z = x +y;
return z;
}
Dr. Yousaf, PIEAS
Pass by Value

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/* Passing arguments by value */
//Page Example 366
#include <stdio.h>
void by_value(int x, int y, int z);
int main()
{
int x = 2, y = 4, z = 6;
printf("n Before calling by_value,
x = %d, y = %d, z = %d.", x, y, z);
by_value(x, y, z);
printf("nn After calling by_value, x
= %d, y = %d, z = %d.",
x, y, z);
getchar();
return(0);
}
void by_value(int x, int y, int z)
{ printf("nn Within function
by_value, x = %d, y = %d, z =
%d.", x, y, z);
x = 0; y = 0; z = 0;
printf("nn Again within
function by_value , x = %d, y =
%d, z = %d.", x, y, z); }
Before calling by_value,
x = 2, y = 4, z = 6.
// Within function by_value,
x = 2, y = 4, z = 6.
// Again Within function
by_value,
x = 0, y = 0, z = 0.
//After calling y_value(),
x = 2, y = 4, z = 6.
Pass by Value

Calling Functions:
Call by Value and Call by Reference
• Used when invoking functions
• Call by value
– Copy of argument passed to function
– Changes in function do not effect original
– Use when function does not need to modify argument
• Avoids accidental changes
• Call by reference
– Passes original argument
– Changes in function effect original
– Only used with trusted functions
• At this stage, we focus on call by value
• We will discuss call by reference later.
Dr. Yousaf, PIEAS

Parameters Passed by Value
• Parameters passed by
value!!
– This means they are
basically local variables
initialized to the values
that the function is
called with.
– They can be modified
as you wish but these
modifications will not
be seen in the calling
routine!
#include<stdio.h>
int twice(int x);
int main()
{
int x=10,y;
y=twice(x);
printf("%d,%dn",x,y);
getchar(); retun 0;
}
int twice(int x)
{
x=x+x;
return x;
}
Dr. Yousaf, PIEAS

Functions can Access Other Functions
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Functions can access other functions
Once you have written a function, it can be accessed
from other functions. We can therefore build more
complex functions from simpler functions
Dr. Yousaf, PIEAS

Dr. Yousaf, PIEAS
// Function calling other function
#include <stdio.h>
float getavg(float x, float y, float z, int totnum);
float calavg(float sum_res, int totalnum);
int main() { float num1 = 3.5, num2 = 5.9, num3 = 1.7, avg;
int totnumbers = 3;
avg = getavg(num1,num2,num3,totnumbers);
printf("Average is %fn",avg); getchar(); return 0; }
float getavg(float x, float y, float z, int totnum)
{ float sum = x + y + z, average;
average = calavg(sum, totnum);
return average;
}
float calavg(float sum_res, int totalnum)
{ float avrg = sum_res/totalnum;
return avrg; }

Calling a function by Another Function
void a(void)
{
printf(“Function a”);
b();
}
void b(void)
{
printf(“Function b”);
}
void main()
{
a();
b();
}
Dr. Yousaf, PIEAS
Can we call function b() inside function a() ?
No, as function a() does not know anything
about function b().
A function can call only those functions
which are defined or declared before it.

More discussion on input and output of
Functions
Dr. Yousaf, PIEAS

// Calculate factorial without function
#include<stdio.h>
int main()
{
int i, fact, num1;
printf("Enter a positive integern");
scanf("%d", &num1);
fact = 1;
for (i = num1; i >=1; i--)
{
fact = fact * i;
}
printf("Factorial of %d is %dn",num1, fact);
getchar();
return 0;
}
Dr. Yousaf, PIEAS

Dr. Yousaf, PIEAS
// Calculate factorial using
//Functions
#include<stdio.h>
int cal_fac(int x);
int main()
{
int i, fact, num1;
printf("Enter a positive integren");
scanf("%d", &num1);
fact = cal_fac(num1);
printf("Factorial of %d is
%dn",num1, fact);
getchar();
return 0;
}
int cal_fac(int x)
{
int i, fact;
fact = 1;
if(x == 0)
fact = 1;
else
{
for (i = x; i >=1; i--)
{
fact = fact*i;
}
}
return fact;
}

Dr. Yousaf, PIEAS
/* demonstrates a function that does
not take any arguments and does not
provide output to main. */
#include <stdio.h>
void stars (); //function declaration
// (prototype)
int main()
{
int x = 5, y = 13;
stars (); //call to function
x = x+10;
y = x*x + (10/2);
}
// function definition
void stars ()
{
int j;
for(j=0; j < 10; j++)
printf("*");
printf("n");
}
Printing stars through a function

Dr. Yousaf, PIEAS
// demonstrates of passing
//constants to a function
#include <stdio.h>
void stars (char ch, int n) ;
int main()
{
int x = 5, y = 13, z;
stars (‘%’, 7); //call to function
x = x+10;
y = x*x + (10/2);
stars (‘$’, 18); //call to function
z = x + y;
return 0;
}
void stars (char ch, int n)
{
int j;
for(j=0; j < n; j++)
printf(“%c“, ch);
printf("n");
}
Printing any symbol any times

Dr. Yousaf, PIEAS
// demonstrates of passing values from
//variables to a function
#include <stdio.h>
void stars (char ch, int n) ;
int main()
{
char chp;
int nt ;
printf(“Please enter a symbol you want
to printn”);
chp = getchar();
printf(“Please enter the number of times
you want to print the charactern”);
scanf(“%d”, nt);
stars (chp, nt); //call to function
// Rest of the code here
return 0;
}
{
int j;
for(j=0; j < n; j++)
printf("n");
}
Passing Variables

Dr. Yousaf, PIEAS
// Demonstration of missing arguments
#include <stdio.h>
void stars (char ch = ‘*’, int n = 10) ;
int main()
{
char chp;
int nt ;
// Rest of the code
stars (‘#’); //call to function
stars (‘+’, 5); //call to function
chp = ‘~’;
nt = 12;
stars (chp, nt); //call to function
stars();
// Rest of the code here
return 0; }
{
int j;
for(j=0; j < n; j++)
printf("n");
}
Missing Arguments

Returning a value from function
Dr. Yousaf, PIEAS
/* Program that will pass temperature in
centigrade to a function that converts it
into Fahrenheit and returns the value to
the main function*/
#include <stdio.h>
float ctof (float); //declaration
int main()
{
float centi, farhen;
printf("nEnter temperature in
centigraden");
scanf("%f",&centi);
farhen = ctof(centi);
printf(“ %f Centigrade = %f Faherenheit”,
centi, fahren);
getchar();
return 0;
}
/* converts centigrade to
Fahrenheit */
float ctof (float cgrade)
{
float fgrade;
fgrade = (9/5)*cgrade+ 32.0;
return fgrade;
}

Arguments and Parameters
• stars (‘%’, 7); //call to function
• Arguments: The values as ‘%’, 7 that are passed to a
function are called arguments.
• void stars (char ch, int n)
• The variables within the function that hold the
arguments are called parameters. In this example, ch
and n are parameters.
• We should note that many programmers use the terms
argument and parameter somewhat interchangeably.
• When the function is called, its parameters are
automatically initialized to the values passed by the
calling program.
Dr. Yousaf, PIEAS

// Finding the maximum of three numbers using a function
#include<stdio.h>
int maximum( int, int, int );
int main()
{
int a, b, c;
printf("Enter three integers: " );
scanf("%d%d%d", &a, &b, &c );
printf( "Maximum is: %dn", maximum( a, b, c ) );
}
int maximum( int x, int y, int z )
{
int max = x;
if ( y > max )
max = y;
if ( z > max )
max = z;
return max;}
Dr. Yousaf, PIEAS

Passing string to a function
#include <stdio.h>
void Display(char ch[]);
int main()
{
char c[50];
printf("Enter string: ");
gets(c);
Display(c); // Passing string c to function.
}
// Function definition
void Display(char ch[]) // It will automatically fix its size
{
printf("String Output: ");
puts(ch);
}
Dr. Yousaf, PIEAS

#include <stdio.h>
void func1(void);
int main()
{
int count;
for (count = 0; count < 20; count++)
{
printf("At iteration %d: ", count);
func1();
}
}
void func1(void)
{
int x = 0;
int y = 0;
printf("x = %d, y = %dn", x, y);
x++;
y++;
}
Dr. Yousaf, PIEAS
• At iteration 0: x = 0, y = 0
• and so on

Scope of Variables
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//Concept of local variables
#include <stdio.h>
void demo(void);
int main()
{
int x = 1, y = 2;
printf("nnBefore calling demo(), x = %d and y = %d", x, y); //x=1, y=2
demo();
printf("nnAfter calling demo(), x = %d and y = %dn", x, y); //x=1,y=2
}
void demo(void) // Function header and definition
{
/* Declare and initialize two local variables. */
int x = 88, y = 99;
/* Display their values. */
printf("nnWithin demo(), x = %d and y = %d", x, y); // x=88, y=89
}
Dr. Yousaf, PIEAS

What is scope?
• The scope of a variable is where it can be used in
a program
LOCAL VARIABLES
• Normally variables are local in scope - this means
they can only be used in the function where they
are declared.
• All variables declared inside functions are local
variables
– Known only in function defined
Dr. Yousaf, PIEAS

Local Variables
• Local Variables
int func1 (int y)
{
int a, b = 10;
float rate;
double cost = 12.55;
.......
}
• Those variables declared “within” the function are
considered “local variables”.
• They values can only be used inside the function they
were declared in, and not elsewhere.
Dr. Yousaf, PIEAS

The print stars example
#include <stdio.h>
void print_stars(int);
int main()
{
int i;
for (i= 0; i < 5; i++)
print_stars(5);
return 0;
}
void print_stars (int n)
{
int i;
for (i= 0; i < n; i++)
printf ("*");
printf ("n");
}
This program prints five rows of
five stars
This prints 'n' stars and then
a new line character
Loop around 5 times to
print the stars
*****
*****
*****
*****
*****
Variables here are LOCAL variables
Dr. Yousaf, PIEAS

Local and Global Variables
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// Scope of variables, Page 80
//Local versus global (external) variables, pages; 207-209
// Local Variable
#include<stdio.h>
void demo(int x);
int main()
{
int x = 10;
printf("n in main, before demo x = %d nn", x); // x = 10
demo(x);
printf("in main, after demo x = %d nn", x); // x = 10
}
void demo (int x)
{
x = x+20;
printf("inside demo x= %d nn", x); // x = 30
}
•
Dr. Yousaf, PIEAS

// Global variable
#include<stdio.h>
void demo();
int x = 10; // note the declaration above the main
int main()
{
printf("nin main, before demo x = %d nn", x); // x = 10
demo();
getchar();
return 0;
}
void demo ()
{
x = x + 20; // x has not been declared in demo
printf("in demo x = %d nn", x); // x = 30
}
Dr. Yousaf, PIEAS

Global Variables
• We can also declare global variables.
• If we declare a variable outside a function it can be
used in any function beneath where it is declared,
hence called global variables.
• Global variables are also sometimes called external
variables, since they are defined external to any
function.
Dr. Yousaf, PIEAS

// Again x is global variable
#include<stdio.h>
void demo(int y); // y is local variable
int x = 10; // x is global variable
int main()
{
demo(x);
getchar();
return 0;
}
void demo (int y) // y has been declared in demo
{
x = y + 20; // x has not been declared in demo
}
Dr. Yousaf, PIEAS

// Still Local variable
#include<stdio.h>
void demo(int x);
int x = 10;
int main()
{
demo(x);
printf("nin main, after demo x = %d nn", x); // x = 10
getchar();
return 0;
}
void demo (int x) // demo has its own x, so now local for this function.
{
x = x + 20;
} Dr. Yousaf, PIEAS

Example: Global Variable
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#include <stdio.h>
float total = 0.0;
void caltot (float num1, float num2,
float num3); //declaration
void printtot ();
int main()
{
float x = 4.5, y = 3.7, z = 8.1;
caltot(x, y, z);
printtot();
printf(“Total is %fn”, total);
getchar();
return 0;
}
void caltot (float num1,
float num2, float num3)
{
total = num1 + num2 +
num3;
}
void printtot ()
{
}

Example: Previous Example Without
Global Variable // Error
Dr. Yousaf, PIEAS
#include <stdio.h>
void caltot (float num1, float num2,
float num3); //declaration
void printtot ();
int main()
{
float x = 4.5, y = 3.7, z = 8.1;
float total = 0.0;
caltot(x, y, z);
printtot();
getchar();
return 0;
}
void caltot (float num1,
float num2, float num3)
{
total = num1 + num2 +
num3; // error
}
void printtot ()
{
// error
}

Notes About Global Variables
– Global variables are also called extern
variables.
– Global variables are known in any function
• A global variable is used when it must be accessible to
more than one function in a program.
• Global variables are often the most important variables
in procedural programs.
• However, global variables create organizational problems
because they can be accessed by any function.
• The wrong functions may access them, or functions may
access them incorrectly.
Dr. Yousaf, PIEAS

Notes About Global Variables
Question:
Can there be a local and a global variable of same name?
Ans:
Yes, if a function has a variable whose name is same as
previously declared global variable, then the local
variable will take precedence inside such a function
Dr. Yousaf, PIEAS

Home Take Assignment
(1) Declare a global array of 10 integers, declare a variable size that
will store the size of the array, now write the following functions.
A. void PrintArray(void) : This function should print the global array
B. void SumArray(void): This function should print the sum of all
elements of the array
(2) A palindrome is a number that reads the same from left to right or
from right to left. For example 121 , 222, 62226 are all palindrome
numbers.
Write a program (without function) that should accept three digits
number from the user. You code should tell whether the given number
is palindrome or not?
(3) Modify the above program such that it should accept three digits
number from the user. Write a function isPalindrome. Pass the
number provided by the user from main to this function. This function
should determine whether the number is palindrome or not? The
function should return the result to the main. The main should display
it.
Dr. Yousaf, PIEAS

Home Take Assignment
A stack is a container of objects such that objects are placed on top of
each other just like dishes are placed on top of each other.
Write a program that declares a global array of 10 integers, name this
array as stack. 2‐ Write the following functions
1‐push: This function should put the value of a variable to the stack.
2‐pop: This function should return the first element of the array
3‐show: The function should display the contents of the array stack
4-shift_right : This function should shift the elements of the array 1
place toward right i.e. element at index 0 will move to index 1 ,
element at index 1 will move to index 2 and so on till the last array
element is processed
5. void shift_left(void) : this function should shift the elements of the
array 1 place towards left i.e. element at index 1 will be shifted to
index 0, element at index 2 will be shifted to index 1.
Dr. Yousaf, PIEAS

C Language Lecture 17

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C Language Lecture 17