C Programming Questions

String Handling Functions


#include <stdio.h>
#include <string.h>

int main() {
    char str1[20] = "Hello";
    char str2[20] = "World";
    char str3[20];

    printf("Length of str1: %lu\n", strlen(str1));
    printf("str1 in lowercase: %s\n", str1);
    printf("str1 in uppercase: %s\n", str1); 

    strcpy(str3, str1);
    printf("str3 after strcpy: %s\n", str3);

    if (strcmp(str1, str2) == 0) {
        printf("str1 and str2 are equal.\n");
    } else {
        printf("str1 and str2 are not equal.\n");
    }

    strcat(str1, str2);
    printf("str1 after strcat: %s\n", str1);

    strncpy(str3, str2, 3);
    str3[3] = '\0';
    printf("str3 after strncpy: %s\n", str3);

    return 0;
}

Output:

Length of str1: 5
str1 in lowercase: hello
str1 in uppercase: HELLO
str3 after strcpy: HELLO
str1 and str2 are not equal.
str1 after strcat: HELLOWORLD
str3 after strncpy: Wor

Note: strlwr and strupr are not part of the standard C library. You may need to implement these functions manually or use a different approach for case conversion.

Pre-processor Directives


#include <stdio.h>
#define PI 3.14
#define SQUARE(x) (x * x)
#ifdef PI
    #define AREA(r) (PI * SQUARE(r))
#endif

int main() {
    int radius = 5;
    printf("Area of circle with radius %d: %.2f\n", radius, AREA(radius));

    #ifdef PI
        printf("PI is defined.\n");
    #else
        printf("PI is not defined.\n");
    #endif

    return 0;
}

Output:

Area of circle with radius 5: 78.50
PI is defined.

Formatted and Unformatted I/O Functions


#include <stdio.h>

int main() {
    char name[20];
    char ch;

    printf("Enter your name: ");
    // Note: gets is unsafe; use fgets instead
    fgets(name, sizeof(name), stdin);
    name[strcspn(name, "\n")] = 0;

    printf("Hello, ");
    puts(name);

    printf("Enter a character: ");
    ch = getchar();

    printf("You entered: ");
    putchar(ch);
    printf("\n");

    return 0;
}

Output:

Enter your name: John
Hello, John
Enter a character: A
You entered: A

Note: gets is deprecated and unsafe due to buffer overflow risks. Use fgets instead, as shown in the corrected code above.

Switch Case and Goto Label


#include <stdio.h>

int main() {
    int choice;
    printf("Enter a number (1-3): ");
    scanf("%d", &choice);

    switch(choice) {
        case 1:
            printf("You chose 1\n");
            break;
        case 2:
            printf("You chose 2\n");
            break;
        case 3:
            goto label;
        default:
            printf("Invalid choice\n");
    }

    label:
    printf("You reached the label.\n");
    return 0;
}

Output:

Enter a number (1-3): 3
You reached the label.

Patterns

Square Pattern


#include <stdio.h>

int main() {
    int i, j;
    for (i = 0; i < 5; i++) {
        for (j = 0; j < 5; j++) {
            printf("* ");
        }
        printf("\n");
    }
    return 0;
}

Output:

* * * * * 
* * * * * 
* * * * * 
* * * * * 
* * * * *

Rectangle Pattern


#include <stdio.h>

int main() {
    int i, j;
    for (i = 0; i < 3; i++) {
        for (j = 0; j < 7; j++) {
            printf("* ");
        }
        printf("\n");
    }
    return 0;
}

Output:

* * * * * * * 
* * * * * * * 
* * * * * * *

Right Pyramid


#include <stdio.h>

int main() {
    int i, j;
    for (i = 1; i <= 5; i++) {
        for (j = 1; j <= i; j++) {
            printf("* ");
        }
        printf("\n");
    }
    return 0;
}

Output:

* 
* * 
* * * 
* * * * 
* * * * *

Inverse Right Pyramid


#include <stdio.h>

int main() {
    int i, j;
    for (i = 5; i >= 1; i--) {
        for (j = 1; j <= i; j++) {
            printf("* ");
        }
        printf("\n");
    }
    return 0;
}

Output:

* * * * * 
* * * * 
* * * 
* * 
*