This is a presentation of c programming which is taught at indian institute of technology kanpur in the first year first semester under the bachelor of technology or bachelor of science programme. ESC basically refers to the fundamentals of computing which here the course is taught by professors under computer science department. Here tutorials are also conducted where tutor comes and solves the doubts of students. To practice programming iit kanpur has its own platform called prutor where all the lab work and practice is done. The content which is taught here is of very good level. To take admission in indian institute of technology of kanpur you have to give joint entrance examination . first you have to give jee mains and then give jee advanced. Well jee advanced is the the toughest exams in the world. Because difficult questions from physics chemistry and maths are asked in it.

1. How to store lots of values of same type?
 We have seen many data types so far
 int, float, char, etc.
 We can use a variable to store a single value of some data type, e.g.,
 int x = 2; // variable x stores one integer value
 float x = 2.3; // variable x stores a one float value
 char x = ‘c’; // variable x stores one char value
 What if we want to store several values, all of same data type?
 Example 1: Marks of all ESC101 students in Major Quiz 1 (all floats)
 Example 2: Roll numbers of all ESC101 students (all int)
 Example 3: Final grade of all ESC101 students (all char)
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2. How to store lots of values of same type?
 Consider storing Minor Quiz marks of all ESC111 students
 This is very time consuming, inelegant, and boring
 Arrays provide a better and more efficient way of doing such things
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float marks1, marks2, marks3, .... ,marks500;
scanf(“%f”, &marks1);
scanf(“%f”, &marks2);
...
scanf(“%f”, &marks500);

3. Arrays
 Not a new data type but a “data structure” (a collection of variables)
 Enables storing multiple values of the same data type
 Specification/declaration of an array needs the following
 A data type (data type of values to be stored; all must be of same type)
 A name (same naming convention as variables)
 A size (how many values to be stored)
 An example of array declaration:
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float marks[500];
Data type
Name Size
Size is an integer in
square brackets

4. Arrays: Basic Syntax
 Each value within the array is called “element” of the array
 Each element is accessed using a non-negative integer-valued index
 First index is 0 (index of first element)
 Last index is array size minus one (index of last element)
 Syntax to access/use each element of the array
name_of_array[index]
 For example:
 marks[0] is the first element of an array named marks
 marks[1] is the second element of array marks
 marks[499] is the last element of array marks 4
Index is an
integer in square
brackets
In some other languages
(such as Python), array
indexing starts with 1

5. Arrays: Basic Syntax
 Array index needs to be within limits (0 to array size - 1)
 For an array declared as marks[500]
 Index -1 is invalid (may give segmentation fault, also known as “segfault”)
 Index 510 is invalid (may give segfault)
 Index 500 is also invalid (recall that 499 is the index of last element)
 Array index need not be a constant integer,
 Can also be a variable/expression (but only int)
 Example: marks[i] or marks[2*i + 1] where i is an integer
 Never use a float/double as index
5

6. Arrays: Storage in memory
 A single variable (int/float/char etc) is stored in a single box in memory
 An array is stored in several consecutive boxes in memory (number of
these boxes is equal to the size of the array)
 More on storage of arrays when we study Pointers
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int a = 2;
float b = 3.2;
a b
2 3.2
float marks[500];
marks[0] marks[1] marks[2] marks[499]
Array name is like street
name, index is like house
number

7. Array: Declaration and Initialization
Can be initialized at time of declaration itself
Can be partly initialized as well
However, if not initialized in same line with declaration, have
to be initialized one by one!
int a[6] = {3,7,6,2,1,0};
int a[6] = {3,7,6};
a 3 7 6 2 1 0
a 3 7 6
int a[6];
a = {3,7,6,2,1,0};
int a[6];
a[2] = 6;
Array elements are
comma separated
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8. Array: Declaration and Initialization
Can be initialized at time of declaration itself
Can be partly initialized as well
Over initialization may crash
Better way to initialize is the following
Warning: uninitialized arrays contain garbage, not zeros
int a[6] = {3,7,6,2,1,0};
int a[6] = {3,7,6};
a 3 7 6 2 1 0
a 3 7 6
int a[6] = {1,2,3,4,5,6,7,8,9};
int a[] = {1,2,3,4,5,6,7,8,9};
I will figure out how
much space needed
No need to specify
the array size during
declaration
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9. Array: Declaration and Initialization
 Can declare the array first and initialize its elements later
 The later initialization can be done using user-provided values (e.g.,
using scanf), or some expression, or using some fixed values
int i,tmp,a[5];
for(i=0;i<5;i++){
scanf(“%d”,&tmp);
a[i] = tmp;
}
Read a use-
provided value
Assign the read
value to the ith
element of the
array
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Can I run the
loop as
for(i=1;i<=5;i++)?
Yes, if you use
a[i-1] = tmp; in
loop’s body

10. Array: Declaration and Initialization
 Can declare the array first and initialize its elements later
 The later initialization can be done using user-provided values (e.g.,
using scanf), or some expression, or using some fixed value
int i,a[5];
for(i=0;i<5;i++){
scanf(“%d”,&a[i]);
}
Directly read a user
provided value into the
ith element of the array
(the tmp variable is not
needed)
Note: &a[i] is evaluated
as &(a[i]) since [] has
higher precedence than &
A shortcut for
reading user
provided
values 10

11. Operator Name Symbol/Sign Associativity
Brackets, array subscript, Post
increment/decrement
(), [] ++, -- Left
Unary negation, Pre
increment/decrement, NOT
-, ++, --, ! Right
Multiplication/division/
remainder
*, /, % Left
Addition/subtraction +, - Left
Relational <, <=, >, >= Left
Relational ==, != Left
AND && Left
OR || Left
Conditional ? : Right
Assignment, Compound
assignment
=, +=, -=, *=, /=,
%=
Right
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12. Array: Declaration and Initialization
 Can declare the array first and initialize its elements later
 The later initialization can be done using user-provided values (e.g.,
using scanf), or some expression, or using some fixed value
int i,a[5];
for(i=0;i<5;i++){
a[i] = i+1;
}
Assign a value of
expression i+1 to
the ith element of
the array
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1 2 3 4 5
a[0] a[1] a[2] a[3] a[4]

13. Array: Declaration and Initialization
 Can declare the array first and initialize its elements later
 The later initialization can be done using user-provided values (e.g.,
using scanf), or some expression, or using some fixed value
Assign a fixed
(constant) value 10
to the ith element of
the array
int i,a[5];
for(i=0;i<5;i++){
a[i] = 10;
}
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10 10 10 10 10
a[0] a[1] a[2] a[3] a[4]

14. Tracing the execution of an array based program
include <stdio.h>
int main () {
int a[5];
int i;
for (i=0; i < 5; i= i+1) {
a[i] = i+1;
}
return 0;
}
a[0] a[1] a[2] a[3] a[4]
i
Let us trace the
execution of the program.
0
Statement becomes a[0] =0+1;
Statement becomes a[1] =1+1;
Statement becomes a[2] =2+1;
1
1
2
2
3
3
Statement becomes a[3] = 3+1;
Statement becomes a[4] = 4+1;
4
4
5
5
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15. Arrays: Some Example Programs
 Create an integer array of size 100
 Initialize elements with even index as 0
 Initialize elements with odd index as 1
int i,a[100];
for(i=0; i<100; i=i+1){
if(i%2==0) a[i] = 0;
else a[i] = 1;
}
Method 1
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16. Arrays: Some Example Programs
 Create an integer array of size 100
 Initialize elements with even index as 0
 Initialize elements with odd index as 1
int i,a[100];
for(i=0; i<100; i=i+2){
a[i] = 0;
a[i+1] = 1;
}
Method 2,
without if-else
Incrementing the
loop counter by 2
This for loop will run
50 times. Each
iteration will assign
values to 2 elements,
one at odd index,
one at even index
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17. Arrays: Some Example Programs
 Check whether a sequence of numbers is a palindrome sequence
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Greek origin word:
palin = again,
dromos = direction
Palindrome: Forward and
Reverse gives the same
sequence
Some palindromes:
1 2 3 4 5 4 3 2 1
1 2 3 3 2 1
Some non-palindromes:
1 2 3 4 5
1 2 3 3 4 1
9 0 4 0 8
int main(){
int a[100], temp, len = 0, i, flag = 1;
while(1){
scanf("%d", &temp);
if(temp == -1)
break;
a[len++] = temp;
}
for(i = 0; i < len; i++)
if(a[i] != a[len-i-1])
flag = 0;
if(flag) printf("YES");
else printf("NO");
return 0;
}
The while(1) loop keeps reading numbers
until user enters -1, store each number as
an element of the array named a
After the while(1) loop exits, len is the
size of the array (indices are 0 to len-1)
This line does a[len] = temp;
and then increments len
a[0] a[1] a[2] a[len-1]
a[len-2]
Compares a[0] with a[len-1], then a[1]
with a[len-2], and so on. If any pair does
not match, set flag variable to 0
flag = 1 assumes that sequence is
palindrome (set 0 if later found otherwise)
Let’s specify a maximum
sequence size

18. Arrays: Some Example Programs
#include <stdio.h>
int main() {
char s[100];
int count = 0;
int ch;
int i;
return 0;
}
ch = getchar();
while ( ch != EOF && count < 100) {
s[count] = ch;
count = count + 1;
ch = getchar();
}
i = count-1;
while (i >=0) {
putchar(s[i]);
i=i-1;
}
/*print_in_reverse */
/*read_into_array */
/* the array of 100 char */
/* counts number of input chars read */
/* current character read */
/* index for printing array backwards */
Read until user has
entered 100 chars or
the end-of-file (EOF)
special character
has been read.
Now print the characters
in reverse order
getchar() returns a
single character
entered by the user
putchar() prints a single character
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