C Programming

• Write a C program print hollow rectangular star pattern of n rows and m columns.

For a hollow rectangular star pattern of 4 rows and 12 columns. Program’s output should be:

Required Knowledge

• For Loop
• printf and scanf function in C

Algorithm to print hollow rectangular star pattern using loop

The algorithm of this pattern is similar to rectangular star pattern except here we have to print stars of first and last rows and columns only. At non-boundary position, we will only print a space character.

• Take the number of rows(N) and columns(M) of rectangle as input from user using scanf function.
• We will use two for loops to print empty rectangular star pattern.
  • Outer for loop will iterate N times. In each iteration, it will print one row of pattern.
  • Inside inner for loop, we will add a if statement check to find the boundary positions of the pattern and print star (*) accordingly.

Here is the matrix representation of the hollow rectangle star pattern. The row numbers are represented by i whereas column numbers are represented by j.

C program to print hollow rectangular star pattern

#include<stdio.h>
 
int main(){
    int rows, cols , i, j;
     
    printf("Enter rows and columns of rectangle\n");
    scanf("%d %d", &rows, &cols);
     
    /* Row iterator for loop */
    for(i = 0; i < rows; i++){
     /* Column iterator for loop */
        for(j = 0; j < cols; j++){
            /* Check if currely position is a boundary position */
            if(i==0 || i==rows-1 || j==0 || j==cols-1)
                printf("*");
            else
                printf(" ");
        }
        printf("\n");
    }
    return 0;
}

Output

Enter rows and columns of rectangle
4 12
************
*          *
*          *
************

• Write a C program to print triangle and pyramid star pattern.

This Program first takes the numbers of rows in pattern and then prints the corresponding pattern using nested for loops. This kind of problems are useful for beginners to understands the fundamentals of loops and spaces. Here, we will discuss about four variations of patterns using ‘*’ character, right triangle, inverted right triangle, pyramid and inverted pyramid.

C program to print triangle pattern using * and loop

In this program, we first take the number of rows in the pattern as input from user using scanf function. Then we use two for loops to print triangle pattern. Outer for loop prints one horizontal row of pattern in one iteration whereas inner for loop prints n stars for n^th row in one iteration.

/*
* C program to print triangle pyramid pattern using *
*/
#include<stdio.h>
#include<conio.h>
 
int main() {
    int i,j,rows;
    printf("Enter the number of rows\n");
    scanf("%d", &rows);
     
    for(i = 1; i <= rows; i++) {
    /* Prints one row of triangle */
        for(j = 1; j <= i; ++j) {
           printf("* ");
        }
        printf("\n");
    }
    getch();
    return 0;
}

Program Output

Enter the number of rows
6
*
* *
* * *
* * * *
* * * * *
* * * * * *

C program to print inverted triangle pattern using * and loop

This c program is similar to above program, the only difference is the pattern is inverted. For i^th row we are printing (rows – i + 1) starts.

For Example

Let, total number of rows in pattern is 6 then.
Number of starts in 3th row = 6 – 3 + 1 = 4

/*
* C program to print inverted half pyramid pattern using *
*/
#include<stdio.h>
#include<conio.h>
 
int main() {
    int i,j,rows;
    printf("Enter the number of rows\n");
    scanf("%d", &rows);
     
    for(i = rows; i > 0; i--) {
    /* Prints one row of triangle */
        for(j = i; j > 0; j--) {
           printf("* ");
        }
        printf("\n");
    }
    getch();
    return 0;
}

Program Output

Enter the number of rows
6
* * * * * *
* * * * *
* * * *
* * * 
* *
*

C program to print pyramid pattern using * and loop

In this program, we are printing a pyramid pattern in which i^th row contains (2*i – 1) space separated stars. We first take the number of rows in the pattern as input from user using scanf function. One iteration of outer for loop will print a row of pyramid. Inner for loop prints the initial spaces for every line and nested while loop prints (2*r – 1) space separated stars for r^th row of pyramid.

/*
* C Program to print full pyramid pattern using *
*/
#include<stdio.h>
#include<conio.h>
int main() {
    int row, space, rows, star=0;
    printf("Enter the number of rows in pyramid\n");
    scanf("%d",&rows);
 
    for(row = 1;row <= rows; row++) {
     /* Printing spaces */
        for(space = 1; space <= rows-row; space++) {
           printf("  ");
        }
        /* Printing stars */
        while(star != (2*row - 1)) {
            printf("* ");
            star++;;
        }
        star=0;
        printf("\n");
    }
    getch();
    return 0;
}

Program Output

Enter the number of rows in pyramid
5 
       *
      * * *
    * * * * *
  * * * * * * *
* * * * * * * * *

C program to print inverted pyramid pattern using * and loop

/*
* C Program to print full pyramid pattern using *
*/
#include<stdio.h>
#include<conio.h>
int main() {
    int row, space, rows, star=0;
    printf("Enter the number of rows in reverse pyramid\n");
    scanf("%d",&rows);
 
    for(row = rows;row >= 1; row--) {
     /* Printing spaces */
        for(space = 0; space <= rows-row; space++) {
           printf("  ");
        }
        /* Printing stars */
        star = 0;
        while(star != (2*row - 1)) {
            printf("* ");
            star++;
        }
        printf("\n");
    }
    getch();
    return 0;
}

Program Output

Enter the number of rows in reverse pyramid
5 
* * * * * * * * *
  * * * * * * *
    * * * * *
      * * *
        *

• Write a C program to print all prime numbers between 1 to N using for loop.
• Wap in C to print prime numbers between 1 to 100.

Required Knowledge

• C printf and scanf functions
• For loop in C

A Prime number is a natural number greater than 1 that is only divisible by either 1 or itself. All numbers other than prime numbers are known as composite numbers. There are infinitely many prime numbers, here is the list of first few prime numbers
2 3 5 7 11 13 17 19 23 29 31 37….

Algorithm to check whether a number is prime number or not

• Let, N be a positive number.
• For every number i, between 2 to N/2(2<= i <= N/2) check whether i divides N completely(check If i is a factor of N).
• if (N % i == 0), then N cannot be a Prime number.
• If none of the number between 2 to N/2 divides N completely then N is a prime number.

C program to print all prime numbers between 1 to N using for loop

#include<stdio.h>
#include<conio.h>
  
int main(){
  
    int N, i, j, isPrime, n;
     
    printf("To print all prime numbers between 1 to N\n");
    printf("Enter the value of N\n");
    scanf("%d",&N);
  
    /* For every number between 2 to N, check 
    whether it is prime number or not */
    printf("Prime numbers between %d to %d\n", 1, N);
     
    for(i = 2; i <= N; i++){
        isPrime = 0;
        /* Check whether i is prime or not */
        for(j = 2; j <= i/2; j++){
             /* Check If any number between 2 to i/2 divides I 
              completely If yes the i cannot be prime number */
             if(i % j == 0){
                 isPrime = 1;
                 break;
             }
        }
          
        if(isPrime==0 && N!= 1)
            printf("%d ",i);
    }
   getch();
   return 0;
}

Output

To print all prime numbers between 1 to N
Enter the value of N
50
Prime numbers between 1 to 50
2 3 5 7 11 13 17 19 23 29 31 37 41 43 47

• C programming language supports various operators to perform various operations like logical, mathematical, relational, arithmetic, bitwise operators etc. In this tutorial we will learn about various C operators in brief with sample programs.

An operator in C is a symbol used to perform logical and mathematical operations in a C program.

A statement containing operators and variables is called an Expression. C operators connects constants and variables to form expressions.
For Example

In 2 x (length + breadth);

• x and + are operators
• 2 is a constant
• length and breadth are variables
• “2x(length + breadth)” is an expression, performing one logical task

C programming language is rich in built in operators. Here is the list of operators supported by C language.

• Arithmetic Operators
• Assignment Operators
• Bitwise Operators
• Logical Operators
• Relational Operators
• Conditional Operator

Special Operators in C

Below are some special operators supported by C language.

Address of Operator(&)
The & is a unary operator in C which returns the memory address of the passed operand. This is also known as “address of” operator.

A pointer contains the memory address of some object.

Value of Operator(*)
The * is a unary operator which returns the value of object pointer by a pointer variable. It is known as value of operator.

It is also used for declaring pointer variable.

For Example
int A = 100;
int *ptr = &A;
In the first statement, we first declare an integer variable and initialize it with value 100. In second statement, we are declaring a pointer to a variable of type int and initializing it with address of A.

Sizeof Operator
The sizeof is a compile time operator not a standard library function. The sizeof is a unary operator which returns the size of passed variable or data type in bytes.

As we know, that size of basic data types in C is system dependent, So we can use sizeof operator to dynamically determine the size of variable at run time.

C program to show use of Sizeof, & and * Operator

#include<stdio.h>
#include<conio.h>
 
int main()
{
    int A = 10;
    /* Use of & and * Operator */
    int *ptr = &A;
    printf("Value of A is %d\n", *ptr);
     
    /* Use of Sizeof Operator to dynamically determine
       the size of data types and variables */
    printf("Size of variable A is %d\n", sizeof(A));
    printf("Size of an Integer variable is %d\n", sizeof(int));
    printf("Size of long int variable is %d\n", sizeof(long int));
    printf("Size of char variable is %d\n", sizeof(char));
    printf("Size of float variable is %d\n", sizeof(float));
     
    getch();
    return(0);
}

Output

Value of A is 10
Size of variable A is 4
Size of an Integer variable is 4
Size of long int variable is 4
Size of char variable is 1
Size of float variable is 4

Operator Precedence

An expression in C may contains more than one variables and operators. Not every operator in C is of same precedence, some operators are of higher priority than others; for example increment operator(++) is of higher precedence than addition operator(+). Operator precedence defines the sequence of evaluation for operators of an expression, to resolve and ambiguity.
For Example
X = 1 + 2 * 3;

Without any Operator precedence, above expression can be evaluated in two different ways producing two different values for X.

Performing addition before multiplication
X = 3 * 3 = 9

Performing multiplication before addition
X = 1 + 6 = 7

To resolve this confusion, we assign different precedence to different operator. As the precedence of multiplication is more than addition, Correct value of X is 7.

The associativity specifies the operators direction to be evaluated, it may be left to right or right to left.

Below table lists the operators in decreasing order of their precedence.

A header file in C programming language is a file with .h extension which contains a set of common function declarations and macro definitions which can be shared across multiple program files. C language provides a set of in build header files which contains commonly used utility functions and macros.

For Example:

• stdio.h header file contains standard Input and Output functions.
• string.h header file contains string handling functions.

Types of Header Files in C

• User defined header files.
• In-built header files.

#inclide Preprocessor Directives is used to include both system header files and user defined header files in C Program.

Syntax to Include Header File in C Program

#include <Header_file_name>

Above mentioned #include syntax is used to include in-built system header files. It searches given header file in a standard list of directories where all in-built header files are stored. To include in-built header file we use triangular bracket.

#include "Header_file_name"

Above mentioned #include syntax is used to include user-defined system header files. It searches given user defined header file in a current directories where current c program exists. To include user-defined header file we use double quotes.

For Example:

#include <math.h>          // Standard Header File
#include "myHeaderFile.h"    // User Defined Header File

Including a header file in a c program is equivalent to copying the content of the header file in your program. Above statement tells the preprocessor to replace this line with content of math.h header file.

Create Your Own Header File in C

Steps to create your own header file

1. Open a text editor and type a function definition, like we define a new function in C program.

   int getSquare(int num){
      return num*num;
   }

2. Save this file with .h extension. Lets assume we saved this file as myMath.h.
3. Copy myMath.h header file to the same directory where other inbuilt header files are stored.
4. Compile this file.
5. To Include your new header file in a c program used #include preprocessor directive.

   #include "myMath.h"

6. Now you can directly call any function define inside myMath.h header file.

#include <stdio.h>
#include "myMath.c" 
 
int main(){
    int number;
     
    printf("Enter an Integer\n");
    scanf("%d", number);
    printf("Square of %d is %d\n", number, getSquare(number));
     
    return 0;
}

#if Condition_One
   # include "headerFile_One.h"
#elif Condition_Two
   # include "headerFile_Two.h"
#elif Condition_Three
   # include "headerFile_Three.h"
  .
  .
#endif

Write a program in c to swap the content of two strings

• Write a C program to swap two strings using strcpy.
• C Program to swap two strings without using extra memory

Given two strings, we have to swap the content of strings. For example, If firstString = “Apple” and secondString = “Banana” then after swapping firstString = “Banana” and secondString = “Apple”. We can either use strcpy to swap two strings using a temporary string or define user defined function to swap two strings.

C program to swap strings using strcpy function

In this program, we first take two string as input from user using gets function. We use a temporary character array tempString to temporarily store a string while swapping content. This program call strcpy function three times.

Algorithm to swap two strings using strcpy

This algorithm of swapping string is similar to the algorithm of swapping integers using a temporary variable. Let firstString and secondString are two input strings and tempString is a temporary string whose size is equal to or more than the size of firstString.

• Copy firstString’s content into tempString using strcpy.
• Copy secondString’s content into firstString using strcpy.
• Copy tempString’s content into secondString.

/*
* C Program to swap two strings
*/
#include <stdio.h>
#include <conio.h>
#include <string.h>
 
int main(){
    char firstString[100], secondString[100], tempString[100];
     
    printf("Enter first String \n");
    gets(firstString);
    printf("Enter second String \n");
    gets(secondString);
    /* Swap strings using a temporary array */
    /* Copy firstString into tempString */   
    strcpy(tempString, firstString);
    /* Copy secondString into firstString */
    strcpy(firstString, secondString);
    /* Copy tempString back to secondString*/
    strcpy(secondString, tempString);
    printf("After Swapping\n");
    printf("First String: %s\nSecond String: %s", firstString, secondString);
 
    getch();
    return 0;
}

Program Output

Enter first String
Apple
Enter second String
Banana
After Swapping
First String: Banana
Second String: Apple

C Program to swap two strings without using extra memory

In this program, we don’t use any temporary character array for swapping. We swap the characters of both input strings one by one from index 0 till end of the smaller string and then copy remaining characters of the bigger string.

/*
* C Program to swap two strings using function
*/
#include <stdio.h>
#include <conio.h>
 
void swapStrings(char *firstString, char *secondString);
int main(){
    char firstString[100], secondString[100];
    printf("Enter first String \n");
    gets(firstString);
    printf("Enter second String \n");
    gets(secondString);
     
    swapStrings(firstString, secondString);
    printf("After Swapping\n");
    printf("First String: %s\nSecond String: %s", firstString, secondString);
 
    getch();
    return 0;
}
 
/*
 * Swaps two passed strings 
 */
void swapStrings(char *firstString, char *secondString){
    if(firstString == NULL || secondString == NULL)
        return;
    /* Initialize it to first character index of both string */
    int firstStringIndex = 0, secondStringIndex = 0;
    char temp;
    /* Starting from index 0, keep on swapping characters 
     using a temporay char variable temp*/
    while(firstString[firstStringIndex] != '\0' && secondString[secondStringIndex] != '\0') {
        temp = firstString[firstStringIndex];
        firstString[firstStringIndex] = secondString[secondStringIndex];
        secondString[secondStringIndex] = temp;
        firstStringIndex++;
        secondStringIndex++;
    }
    if(firstString[firstStringIndex] == '\0'){
        /* If firstString ends before secondString, copy the remaining 
          characters of secondString into firstString */
        firstString[firstStringIndex++] = secondString[secondStringIndex];
        secondString[secondStringIndex++] = '\0';
        while(secondString[secondStringIndex] != '\0'){
            firstString[firstStringIndex++] = secondString[secondStringIndex++];
        }
        firstString[firstStringIndex] = '\0';
    } else {
        /* If secondString ends before firstString, copy the remaining 
          characters of firstString into secondString */
        secondString[secondStringIndex++] = firstString[firstStringIndex];
        firstString[firstStringIndex++] = '\0';
        while(firstString[firstStringIndex] != '\0'){
            secondString[secondStringIndex++] = firstString[firstStringIndex++];
        }
        secondString[secondStringIndex] = '\0';
    }
}
</conio.h></stdio.h>

Program Output

Enter first String
TechCrashCourse
Enter second String
CProgramming
After Swapping
First String: CProgramming
Second String: TechCrashCourse