Codes

// Finding string length using strlen

#include <stdio.h>

#include <string.h>

int main()

{

    char a[50];

    int l;

    printf("Enter a string: ");

    gets(a);

    l = strlen(a);

    printf("Length of string is: %d", l);

    return 0;

}

c

Copy code

// Copying a string using strcpy

#include <stdio.h>

#include <string.h>

int main()

{

    char str1[50], str2[50];

    printf("Enter string: ");

    gets(str1);

    strcpy(str2, str1);

    puts(str2);

    return 0;

}

c

Copy code

// Comparing strings using strcmp

#include <stdio.h>

#include <string.h>

int main()

{

    char str1[50], str2[50];

    int c;

    printf("Enter first string: ");

    gets(str1);

    printf("Enter second string: ");

    gets(str2);

    c = strcmp(str1, str2);

    if (c == 0)

        printf("Strings are equal");

    else

        printf("Strings are not equal");

    return 0;

}

c

Copy code

// Concatenation of strings using strcat

#include <stdio.h>

#include <string.h>

int main()

{

    char str1[50], str2[50];

    printf("Enter first string: ");

    gets(str1);

    printf("Enter second string: ");

    gets(str2);

    strcat(str1, str2);

    puts(str1);

    return 0;

}

// String reverse

#include <stdio.h>

#include <string.h>

int main()

{

    char str[50];

    printf("Enter string: ");

    gets(str);

    strrev(str);

    puts(str);

    return 0;

}

2. Finding String Length (User-defined function)

c

Copy code

// Finding string length

#include <stdio.h>

#include <string.h>

int mystrlen(char []);

int main()

{

    char str[50];

    int length;

    printf("Enter a string: ");

    gets(str);

    length = mystrlen(str);

    printf("%d", length);

    return 0;

}

int mystrlen(char str[50])

{

    int i = 0;

    while (str[i] != '\0')

    {

        i++;

    }

    return i;

}

3. String Copying (User-defined function)

c

Copy code

// String copying

#include <stdio.h>

#include <string.h>

void mystrcpy(char str2[50], char str1[50]);

int main()

{

    char str1[50], str2[50];

    printf("Enter string: ");

    gets(str1);

    mystrcpy(str2, str1);

    puts(str2);

    return 0;

}

void mystrcpy(char str2[50], char str1[50])

{

    int s = 0;

    while (str1[s] != '\0')

    {

        str2[s] = str1[s];

        s++;

    }

    str2[s] = '\0';

}

1. String Comparison (User-defined strcmp)

// String comparison
#include <stdio.h>
#include <string.h>

int mystrcmp(char [], char []);

int main()
{
    char str1[50], str2[50];
    int c;

    printf("Enter first string: ");
    gets(str1);

    printf("Enter second string: ");
    gets(str2);

    c = mystrcmp(str1, str2);

    if (c == 0)
        printf("Strings are equal");
    else
        printf("Strings are not equal");

    return 0;
}

// Function definition
int mystrcmp(char str1[50], char str2[50])
{
    int i = 0;

    while (str1[i] != '\0' || str2[i] != '\0')
    {
        if (str1[i] > str2[i])
            return 1;
        else if (str1[i] < str2[i])
            return -1;

        i++;
    }

    return 0;
}

---

2. String Concatenation (User-defined strcat)

// String concatenation
#include <stdio.h>
#include <string.h>

void mystrcat(char str1[50], char str2[50]);

int main()
{
    char str1[50], str2[50];

    printf("Enter first string: ");
    gets(str1);

    printf("Enter second string: ");
    gets(str2);

    mystrcat(str1, str2);
    puts(str1);

    return 0;
}

void mystrcat(char str1[50], char str2[50])
{
    int i, l1, l2;

    l1 = strlen(str1);
    l2 = strlen(str2);

    for (i = 0; i < l2; i++)
    {
        str1[l1 + i] = str2[i];
    }

    str1[l1 + l2] = '\0';
}

---

3. String Reverse (User-defined Function)

// String reverse
#include <stdio.h>
#include <string.h>

void mystrrev(char str[50]);

int main()
{
    char str[50];

    printf("Enter string: ");
    gets(str);

    mystrrev(str);

    printf("Reverse of entered string is: ");
    puts(str);

    return 0;
}

void mystrrev(char str[50])
{
    char temp;
    int i, j, l;

    l = strlen(str);

    for (i = 0, j = l - 1; i <= j; i++, j--)
    {
        temp = str[i];
        str[i] = str[j];
        str[j] = temp;
    }
}

---

4. Use of fflush(stdin)

// Use of fflush(stdin)
#include <stdio.h>

int main()
{
    char str[50];
    int i;

    printf("Enter vowels: ");

    for (i = 0; i < 5; i++)
    {
        fflush(stdin);
        scanf("%c", &str[i]);
    }

    for (i = 0; i < 5; i++)
    {
        printf("%c", str[i]);
    }

    return 0;
}

---

5. Palindrome Check Using String Functions

/* Write a C program to check whether the entered string
   is palindrome or not */
#include <stdio.h>
#include <string.h>

void mystrrev(char [], char []);
int mystrcmp(char [], char []);

int main()
{
    char str1[50], str2[50];
    int c;

    printf("Enter a string: ");
    gets(str1);

    mystrrev(str2, str1);
    c = mystrcmp(str1, str2);

    if (c == 0)
        printf("Entered string is a palindrome");
    else
        printf("Entered string is not a palindrome");

    return 0;
}


String Reverse (Using Another String)
void mystrrev(char str2[50], char str1[50])
{
    int i, l;

    l = strlen(str1) - 1;

    for (i = 0; i <= l; i++)
    {
        str2[i] = str1[l - i];
    }

    str2[i] = '\0';
}


String Comparison (User-defined strcmp)
int mystrcmp(char str1[50], char str2[50])
{
    int i = 0;

    while (str1[i] != '\0' || str2[i] != '\0')
    {
        if (str1[i] > str2[i])
            return 1;
        else if (str1[i] < str2[i])
            return -1;

        i++;
    }

    return 0;
}


Toggle / Invert Case of String
#include <stdio.h>
#include <string.h>

int main()
{
    char str[80];
    int i = 0;

    printf("Enter a string: ");
    gets(str);

    while (str[i] != '\0')
    {
        if (str[i] >= 'A' && str[i] <= 'Z')
            str[i] = str[i] + 32;
        else if (str[i] >= 'a' && str[i] <= 'z')
            str[i] = str[i] - 32;

        i++;
    }

    printf("Toggled string is ");
    puts(str);

    return 0;
}


Count Vowels and Consonants
#include <stdio.h>
#include <string.h>

int main()
{
    char str[50];
    int i = 0, vow = 0, con = 0;

    printf("Enter a string: ");
    gets(str);

    while (str[i] != '\0')
    {
        if (str[i] == 'a' || str[i] == 'A' ||
            str[i] == 'e' || str[i] == 'E' ||
            str[i] == 'i' || str[i] == 'I' ||
            str[i] == 'o' || str[i] == 'O' ||
            str[i] == 'u' || str[i] == 'U')
            vow++;
        else
            con++;

        i++;
    }

    printf("No. of vowels: %d", vow);
    printf("\nNo. of consonants: %d", con);

    return 0;
}


Check Character Type
#include <stdio.h>
#include <string.h>

int main()
{
    char str[50];
    int i = 0;

    printf("Enter a string: ");
    gets(str);

    while (str[i] != '\0')
    {
        if (str[i] >= 'A' && str[i] <= 'Z')
            printf("\n%c is a capital letter", str[i]);
        else if (str[i] >= 'a' && str[i] <= 'z')
            printf("\n%c is a small letter", str[i]);
        else if (str[i] >= '0' && str[i] <= '9')
            printf("\n%c is a digit", str[i]);
        else
            printf("\n%c is a special symbol", str[i]);

        i++;
    }

    return 0;
}


POINTERS
Swap Two Numbers Using Pointers
#include <stdio.h>

void swap(int *, int *);

int main()
{
    int num1, num2;

    printf("Enter 2 numbers: ");
    scanf("%d%d", &num1, &num2);

    printf("Numbers before swapping: %d, %d", num1, num2);
    swap(&num1, &num2);
    printf("\nNumbers after swapping: %d, %d", num1, num2);

    return 0;
}

void swap(int *num1, int *num2)
{
    int temp;

    temp = *num1;
    *num1 = *num2;
    *num2 = temp;
}


Area of Triangle (Call by Reference)
#include <stdio.h>
#include <math.h>

void area(int, int, int, float *);

int main()
{
    int a, b, c;
    float ar = 0.0;

    printf("Enter values of a, b and c: ");
    scanf("%d%d%d", &a, &b, &c);

    area(a, b, c, &ar);
    printf("The area of triangle is: %.2f", ar);

    return 0;
}

void area(int a, int b, int c, float *ar)
{
    int s;

    s = (a + b + c) / 2;

    if (a + b > c && b + c > a && a + c > b)
        *ar = sqrt(s * (s - a) * (s - b) * (s - c));
    else
        printf("Invalid triangle");
}


Reverse Array Using Pointer
#include <stdio.h>

int main()
{
    int arr[50], i, n;
    int *p = arr;

    printf("Enter range: ");
    scanf("%d", &n);

    for (i = 0; i < n; i++)
        scanf("%d", &arr[i]);

    p = &arr[n - 1];

    printf("Reverse: ");
    for (i = 0; i < n; i++)
        printf("%d ", *(p--));

    return 0;
}


Average of Array Using Pointer
#include <stdio.h>

float average(int *, int);

int main()
{
    int arr[50], n, i;
    int *p = arr;

    printf("Enter size of array: ");
    scanf("%d", &n);

    printf("Enter elements:\n");
    for (i = 0; i < n; i++)
        scanf("%d", &arr[i]);

    printf("Average: %.2f", average(p, n));

    return 0;
}

float average(int *p, int n)
{
    int i, sum = 0;

    for (i = 0; i < n; i++)
        sum += *(p++);

    return (float)sum / n;
}


Reverse Array Using Pointer & Function
#include <stdio.h>

void reverse(int *, int);

int main()
{
    int arr[50], n, i;
    int *ap = arr;

    printf("Enter number of elements: ");
    scanf("%d", &n);

    printf("Enter elements: ");
    for (i = 0; i < n; i++)
        scanf("%d", ap + i);

    reverse(ap, n);

    printf("Reversed array:");
    for (i = 0; i < n; i++)
        printf("\n%d", *(ap + i));

    return 0;
}

void reverse(int *ap, int n)
{
    int i, j, temp;

    for (i = 0, j = n - 1; i < j; i++, j--)
    {
        temp = *(ap + i);
        *(ap + i) = *(ap + j);
        *(ap + j) = temp;
    }
}


Armstrong Number Using Pointer
#include <stdio.h>
#include <math.h>

int armstrong(int *);

int main()
{
    int n, *p, temp, sum;

    p = &n;
    printf("Enter a number: ");
    scanf("%d", &n);

    temp = n;
    sum = armstrong(p);

    if (sum == temp)
        printf("Entered number is an Armstrong number");
    else
        printf("Entered number is not an Armstrong number");

    return 0;
}

int armstrong(int *p)
{
    int rem, sum = 0;

    while (*p != 0)
    {
        rem = (*p) % 10;
        sum += pow(rem, 3);
        *p = (*p) / 10;
    }

    return sum;
}




POINTER AND STRING
1. Finding String Length Using Pointer
/* Finding string length using pointer */
#include <stdio.h>
#include <string.h>

int mystrlen(char *);

int main()
{
    char str[50], *s;
    int length;

    printf("Enter a string: ");
    gets(str);

    s = str;
    length = mystrlen(s);

    printf("%d", length);
    return 0;
}

int mystrlen(char *s)
{
    int i = 0;

    while (*s != '\0')
    {
        i++;
        s++;
    }

    return i;
}


2. String Comparison Using Pointer
/* String comparison using pointer */
#include <stdio.h>
#include <string.h>

int mystrcmp(char *, char *);

int main()
{
    char str1[50], str2[50];
    int c;

    printf("Enter first string: ");
    gets(str1);

    printf("Enter second string: ");
    gets(str2);

    c = mystrcmp(str1, str2);

    if (c == 0)
        printf("Strings are equal");
    else
        printf("Strings are not equal");

    return 0;
}

int mystrcmp(char *p1, char *p2)
{
    while (*p1 != '\0' || *p2 != '\0')
    {
        if (*p1 > *p2)
            return 1;
        else if (*p1 < *p2)
            return -1;

        p1++;
        p2++;
    }

    return 0;
}


STRUCTURES
3. Structure Declaration & Initialization
#include <stdio.h>
#include <string.h>

int main()
{
    struct info
    {
        int sno;
        char name[20];
        char add[20];
    } s1, s2;

    struct info stu1 = {1, "ajay", "dehradun"};
    struct info stu2, stu3;

    stu2.sno = 2;
    strcpy(stu2.name, "rashmi");
    strcpy(stu2.add, "delhi");

    printf("Enter sno, name and address of third student:\n");
    scanf("%d%s%s", &stu3.sno, stu3.name, stu3.add);

    printf("\nDetails of students:\n");
    printf("\n1st: %d %s %s", stu1.sno, stu1.name, stu1.add);
    printf("\n2nd: %d %s %s", stu2.sno, stu2.name, stu2.add);
    printf("\n3rd: %d %s %s", stu3.sno, stu3.name, stu3.add);

    return 0;
}


4. Student Information (Single Student)
#include <stdio.h>

int main()
{
    typedef struct
    {
        int sno;
        char name[20];
    } student;

    student s1;

    printf("Enter sno and name: ");
    scanf("%d%s", &s1.sno, s1.name);

    printf("Sno: %d  Name: %s\n", s1.sno, s1.name);
    return 0;
}


5. Student Marks in 4 Subjects
#include <stdio.h>

int main()
{
    typedef struct
    {
        int sno;
        char name[20];
        int submarks[4];
    } student;

    student s1;
    int j;

    printf("Enter sno and name: ");
    scanf("%d%s", &s1.sno, s1.name);

    printf("Enter marks in 4 subjects:\n");
    for (j = 0; j < 4; j++)
        scanf("%d", &s1.submarks[j]);

    printf("Sno: %d Name: %s\n", s1.sno, s1.name);
    for (j = 0; j < 4; j++)
        printf("Subject %d marks: %d\n", j + 1, s1.submarks[j]);

    return 0;
}


6. Information of N Students
#include <stdio.h>

int main()
{
    typedef struct
    {
        int sno;
        char name[20];
        int submarks[4];
    } student;

    student s[10];
    int i, j, n;

    printf("Enter number of students: ");
    scanf("%d", &n);

    for (i = 0; i < n; i++)
    {
        printf("Enter sno and name: ");
        scanf("%d%s", &s[i].sno, s[i].name);

        printf("Enter marks in 4 subjects:\n");
        for (j = 0; j < 4; j++)
            scanf("%d", &s[i].submarks[j]);
    }

    for (i = 0; i < n; i++)
    {
        printf("\nSno: %d Name: %s", s[i].sno, s[i].name);
        for (j = 0; j < 4; j++)
            printf("\nSubject %d marks: %d", j + 1, s[i].submarks[j]);
    }

    return 0;
}


7. Average Percentage of Class
#include <stdio.h>
#include <string.h>

struct stu
{
    char Name[15];
    int Rn;
    float per;
} s1[100];

int main()
{
    int i, n;
    float sumper = 0, avgper;

    printf("Enter number of students: ");
    scanf("%d", &n);

    for (i = 0; i < n; i++)
    {
        fflush(stdin);
        printf("Name: ");
        gets(s1[i].Name);

        printf("Roll no: ");
        scanf("%d", &s1[i].Rn);

        printf("Percentage: ");
        scanf("%f", &s1[i].per);

        sumper += s1[i].per;
    }

    avgper = sumper / n;
    printf("Students scoring >= average:\n");

    for (i = 0; i < n; i++)
    {
        if (s1[i].per >= avgper)
        {
            puts(s1[i].Name);
            printf("Roll no: %d\n", s1[i].Rn);
        }
    }

    return 0;
}


8. Highest Percentage Student
#include <stdio.h>

struct info
{
    int rn;
    char name[20];
    int marks[4];
    float per;
};

int main()
{
    struct info s[50];
    int n, i, j, total, index = 0;
    float high;

    printf("Enter number of students: ");
    scanf("%d", &n);

    for (i = 0; i < n; i++)
    {
        printf("Roll no: ");
        scanf("%d", &s[i].rn);

        fflush(stdin);
        printf("Name: ");
        gets(s[i].name);

        total = 0;
        printf("Enter marks:\n");
        for (j = 0; j < 4; j++)
        {
            scanf("%d", &s[i].marks[j]);
            total += s[i].marks[j];
        }

        s[i].per = (float)total / 4;
    }

    high = s[0].per;
    for (i = 1; i < n; i++)
    {
        if (s[i].per > high)
        {
            high = s[i].per;
            index = i;
        }
    }

    printf("Highest Percentage: %.2f\n", high);
    printf("Name: %s\nRoll no: %d\n", s[index].name, s[index].rn);

    return 0;
}


9. Structure Pointer Example
#include <stdio.h>

int main()
{
    typedef struct
    {
        int rollno;
        char name[20];
    } stud;

    stud s1, s2, *p1, *p2;

    p1 = &s1;
    p2 = &s2;

    printf("First Method:\n");
    scanf("%d%s", &(*p2).rollno, (*p2).name);
    printf("Rollno: %d Name: %s\n", (*p2).rollno, (*p2).name);

    printf("\nSecond Method:\n");
    scanf("%d%s", &(p1->rollno), p1->name);
    printf("Rollno: %d Name: %s\n", p1->rollno, p1->name);

    return 0;
}



UNION
1. Union Example
/* Read and print information using union */
#include <stdio.h>
#include <conio.h>

int main()
{
    union student
    {
        char grade;
        char name[20];
        int roll;
        float per;
    } u1;

    printf("Enter the name:\n");
    gets(u1.name);
    printf("Name -> %s\n", u1.name);

    printf("Enter the roll:\n");
    scanf("%d", &u1.roll);
    printf("Roll no -> %d\n", u1.roll);

    printf("Enter the percentage:\n");
    scanf("%f", &u1.per);
    printf("Percentage -> %f\n", u1.per);

    printf("Enter the grade:\n");
    fflush(stdin);
    scanf("%c", &u1.grade);
    printf("Grade -> %c\n", u1.grade);

    /* Printing complete details (garbage values expected) */
    printf("\nName -> %s", u1.name);
    printf("\nRoll -> %d", u1.roll);
    printf("\nPercentage -> %f", u1.per);
    printf("\nGrade -> %c", u1.grade);

    return 0;
}


2. Memory Allocation: Structure vs Union
#include <stdio.h>
#include <conio.h>

int main()
{
    typedef union
    {
        int roll;
        char grade;
        float per;
    } uni1;

    typedef struct
    {
        int roll;
        char grade;
        float per;
    } str1;

    uni1 u1;
    str1 s1;

    printf("\nSTRUCTURE");
    printf("\nSize of structure: %d", sizeof(s1));
    printf("\nAddress of s1: %u", &s1);
    printf("\nAddress of s1.roll: %u", &s1.roll);
    printf("\nAddress of s1.grade: %u", &s1.grade);
    printf("\nAddress of s1.per: %u", &s1.per);

    printf("\n\nUNION");
    printf("\nSize of union: %d", sizeof(u1));
    printf("\nAddress of u1: %u", &u1);
    printf("\nAddress of u1.roll: %u", &u1.roll);
    printf("\nAddress of u1.grade: %u", &u1.grade);
    printf("\nAddress of u1.per: %u", &u1.per);

    return 0;
}


FILES
3. Store Characters in File & Read
#include <stdio.h>

int main()
{
    FILE *fp1;
    char ch;

    fp1 = fopen("Master.txt", "w");
    if (fp1 == NULL)
    {
        printf("File creation error");
        return 0;
    }

    printf("Enter characters:\n");
    while ((ch = getchar()) != EOF)
    {
        fputc(ch, fp1);
    }
    fclose(fp1);

    fp1 = fopen("Master.txt", "r");
    printf("File contents:\n");
    while ((ch = fgetc(fp1)) != EOF)
    {
        putchar(ch);
    }

    fclose(fp1);
    return 0;
}


4. Copy File Contents
#include <stdio.h>

int main()
{
    FILE *fp1, *fp2;
    char ch;

    fp1 = fopen("Master.txt", "w");
    printf("Enter characters:\n");
    while ((ch = getchar()) != EOF)
        putc(ch, fp1);

    fclose(fp1);

    fp1 = fopen("Master.txt", "r");
    fp2 = fopen("copy.txt", "w");

    while ((ch = getc(fp1)) != EOF)
        putc(ch, fp2);

    fclose(fp1);
    fclose(fp2);

    printf("Copied successfully");
    return 0;
}


5. Convert File Content to Uppercase
#include <stdio.h>
#include <ctype.h>

int main()
{
    FILE *fp1, *fp2;
    char ch;

    fp1 = fopen("source.txt", "w");
    printf("Enter characters:\n");
    while ((ch = getchar()) != EOF)
        putc(ch, fp1);
    fclose(fp1);

    fp1 = fopen("source.txt", "r");
    fp2 = fopen("copy_upper.txt", "w");

    while ((ch = getc(fp1)) != EOF)
    {
        ch = toupper(ch);
        putc(ch, fp2);
    }

    fclose(fp1);
    fclose(fp2);
    return 0;
}


6. Separate Vowels, Consonants, Digits & Special Characters
#include <stdio.h>

int main()
{
    FILE *fp1, *fv, *fc, *fd, *fs;
    char ch;

    fp1 = fopen("Master.txt", "w");
    printf("Enter characters:\n");
    while ((ch = getchar()) != EOF)
        putc(ch, fp1);
    fclose(fp1);

    fp1 = fopen("Master.txt", "r");
    fv = fopen("vowel.txt", "w");
    fc = fopen("consonant.txt", "w");
    fd = fopen("digit.txt", "w");
    fs = fopen("special.txt", "w");

    while ((ch = getc(fp1)) != EOF)
    {
        if (ch=='a'||ch=='e'||ch=='i'||ch=='o'||ch=='u'||
            ch=='A'||ch=='E'||ch=='I'||ch=='O'||ch=='U')
            putc(ch, fv);
        else if ((ch>='A'&&ch<='Z')||(ch>='a'&&ch<='z'))
            putc(ch, fc);
        else if (ch>='0'&&ch<='9')
            putc(ch, fd);
        else
            putc(ch, fs);
    }

    fclose(fp1); fclose(fv); fclose(fc); fclose(fd); fclose(fs);
    return 0;
}


7. Store & Read Integers from File
#include <stdio.h>

int main()
{
    FILE *fp;
    int number;

    fp = fopen("Master.dat", "w");
    printf("Enter integers (Ctrl+Z to stop):\n");

    while (scanf("%d", &number) != EOF)
        putw(number, fp);

    fclose(fp);

    fp = fopen("Master.dat", "r");
    printf("File contents:\n");
    while ((number = getw(fp)) != EOF)
        printf("%d\n", number);

    fclose(fp);
    return 0;
}


8. Separate Even & Odd Numbers
#include <stdio.h>

int main()
{
    FILE *fp, *fe, *fo;
    int num;

    fp = fopen("Master.dat", "w");
    printf("Enter numbers:\n");
    while (scanf("%d", &num) != EOF)
        putw(num, fp);
    fclose(fp);

    fp = fopen("Master.dat", "r");
    fe = fopen("even.dat", "w");
    fo = fopen("odd.dat", "w");

    while ((num = getw(fp)) != EOF)
    {
        if (num % 2 == 0)
            putw(num, fe);
        else
            putw(num, fo);
    }

    fclose(fp); fclose(fe); fclose(fo);
    return 0;
}


9. Store & Read String from File
#include <stdio.h>

int main()
{
    char str[30];
    FILE *fp;

    fp = fopen("test2.txt", "w");
    printf("Enter text:\n");
    while (gets(str) != NULL)
    {
        fputs(str, fp);
        fputs("\n", fp);
    }
    fclose(fp);

    fp = fopen("test2.txt", "r");
    while (fgets(str, 30, fp) != NULL)
        puts(str);

    fclose(fp);
    return 0;
}


10. Count Number of Lines in File
#include <stdio.h>

int main()
{
    FILE *fp;
    char ch;
    int count = 0;

    fp = fopen("test2.txt", "r");
    while ((ch = fgetc(fp)) != EOF)
    {
        if (ch == '\n')
            count++;
    }

    printf("Number of lines: %d", count);
    fclose(fp);
    return 0;
}