Builtin Functions

Introduction

Built-in functions in C are predefined functions provided by the C standard library. These functions perform common tasks and are ready to use without requiring the programmer to write them from scratch. They are included through header files and cover areas like input/output, string manipulation, mathematical operations, memory management, and more.

Key Concepts

Standard Library: Collection of built-in functions provided by C Header Files: Files containing function declarations and definitions Function Prototype: Declaration that specifies function signature Library Linking: Process of connecting library functions to your program

Input/Output Functions (stdio.h)

Basic I/O Functions

#include <stdio.h>

int main() {
    char name[50];
    int age;
    float height;
    
    // Output functions
    printf("Enter your details:\n");
    printf("Name: ");
    
    // Input functions
    scanf("%s", name);
    printf("Age: ");
    scanf("%d", &age);
    printf("Height (in meters): ");
    scanf("%f", &height);
    
    // Formatted output
    printf("\nYour Details:\n");
    printf("Name: %s\n", name);
    printf("Age: %d years\n", age);
    printf("Height: %.2f meters\n", height);
    
    return 0;
}

Character I/O Functions

#include <stdio.h>

int main() {
    char ch;
    
    printf("Enter characters (press 'q' to quit):\n");
    
    while (1) {
        ch = getchar();  // Read single character
        
        if (ch == 'q') {
            break;
        }
        
        printf("You entered: ");
        putchar(ch);     // Print single character
        printf("\n");
    }
    
    return 0;
}

String I/O Functions

#include <stdio.h>

int main() {
    char sentence[100];
    
    printf("Enter a sentence: ");
    gets(sentence);    // Read entire line (deprecated, use fgets instead)
    
    printf("You entered: ");
    puts(sentence);    // Print string with newline
    
    // Safer alternative using fgets
    printf("Enter another sentence: ");
    fgets(sentence, sizeof(sentence), stdin);
    
    printf("You entered: %s", sentence);
    
    return 0;
}

String Functions (string.h)

String Length and Copying

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

int main() {
    char source[] = "Hello World";
    char destination[50];
    char append_str[] = " - Welcome!";
    
    // String length
    int length = strlen(source);
    printf("Length of '%s': %d\n", source, length);
    
    // String copy
    strcpy(destination, source);
    printf("Copied string: %s\n", destination);
    
    // String concatenation
    strcat(destination, append_str);
    printf("After concatenation: %s\n", destination);
    
    return 0;
}

String Comparison and Search

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

int main() {
    char str1[] = "apple";
    char str2[] = "banana";
    char str3[] = "apple";
    char search_str[] = "Hello World Programming";
    char *ptr;
    
    // String comparison
    int result1 = strcmp(str1, str2);
    int result2 = strcmp(str1, str3);
    
    printf("Comparing '%s' and '%s': %d\n", str1, str2, result1);
    printf("Comparing '%s' and '%s': %d\n", str1, str3, result2);
    
    // String search
    ptr = strstr(search_str, "World");
    if (ptr != NULL) {
        printf("'World' found at position: %ld\n", ptr - search_str);
    }
    
    // Character search
    ptr = strchr(search_str, 'o');
    if (ptr != NULL) {
        printf("First 'o' found at position: %ld\n", ptr - search_str);
    }
    
    return 0;
}

Advanced String Functions

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

int main() {
    char str[] = "apple,banana,orange,grape";
    char copy_str[50];
    char *token;
    
    // Safe string copy with size limit
    strncpy(copy_str, str, sizeof(copy_str) - 1);
    copy_str[sizeof(copy_str) - 1] = '\0';
    
    printf("Original: %s\n", str);
    printf("Copy: %s\n", copy_str);
    
    // String tokenization
    printf("\nTokens:\n");
    token = strtok(copy_str, ",");
    while (token != NULL) {
        printf("- %s\n", token);
        token = strtok(NULL, ",");
    }
    
    return 0;
}

Mathematical Functions (math.h)

Basic Mathematical Operations

#include <stdio.h>
#include <math.h>

int main() {
    double x = 16.0, y = 3.0, z = -5.5;
    
    // Power and square root
    printf("%.2f raised to power %.2f = %.2f\n", x, y, pow(x, y));
    printf("Square root of %.2f = %.2f\n", x, sqrt(x));
    
    // Absolute values
    printf("Absolute value of %.2f = %.2f\n", z, fabs(z));
    
    // Ceiling and floor
    printf("Ceiling of %.2f = %.2f\n", z, ceil(z));
    printf("Floor of %.2f = %.2f\n", z, floor(z));
    
    // Logarithmic functions
    printf("Natural log of %.2f = %.2f\n", x, log(x));
    printf("Base-10 log of %.2f = %.2f\n", x, log10(x));
    
    return 0;
}

Trigonometric Functions

#include <stdio.h>
#include <math.h>

#define PI 3.14159265359

int main() {
    double angle_degrees = 45.0;
    double angle_radians = angle_degrees * PI / 180.0;
    
    printf("Angle: %.2f degrees (%.4f radians)\n", angle_degrees, angle_radians);
    
    // Trigonometric functions
    printf("sin(%.2f°) = %.4f\n", angle_degrees, sin(angle_radians));
    printf("cos(%.2f°) = %.4f\n", angle_degrees, cos(angle_radians));
    printf("tan(%.2f°) = %.4f\n", angle_degrees, tan(angle_radians));
    
    // Inverse trigonometric functions
    double value = 0.5;
    printf("\nasin(%.2f) = %.2f degrees\n", value, asin(value) * 180.0 / PI);
    printf("acos(%.2f) = %.2f degrees\n", value, acos(value) * 180.0 / PI);
    printf("atan(%.2f) = %.2f degrees\n", value, atan(value) * 180.0 / PI);
    
    return 0;
}

Memory Management Functions (stdlib.h)

Dynamic Memory Allocation

#include <stdio.h>
#include <stdlib.h>

int main() {
    int *numbers;
    int size = 5;
    
    // Allocate memory
    numbers = (int*)malloc(size * sizeof(int));
    
    if (numbers == NULL) {
        printf("Memory allocation failed!\n");
        return 1;
    }
    
    // Initialize and display
    printf("Enter %d numbers:\n", size);
    for (int i = 0; i < size; i++) {
        scanf("%d", &numbers[i]);
    }
    
    printf("Numbers entered: ");
    for (int i = 0; i < size; i++) {
        printf("%d ", numbers[i]);
    }
    printf("\n");
    
    // Reallocate for more numbers
    size = 8;
    numbers = (int*)realloc(numbers, size * sizeof(int));
    
    if (numbers == NULL) {
        printf("Memory reallocation failed!\n");
        return 1;
    }
    
    printf("Memory reallocated for %d numbers\n", size);
    
    // Free memory
    free(numbers);
    printf("Memory freed\n");
    
    return 0;
}

Utility Functions

#include <stdio.h>
#include <stdlib.h>

int main() {
    char str_number[] = "12345";
    char str_float[] = "123.45";
    
    // String to number conversion
    int number = atoi(str_number);
    float decimal = atof(str_float);
    
    printf("String '%s' to integer: %d\n", str_number, number);
    printf("String '%s' to float: %.2f\n", str_float, decimal);
    
    // Random number generation
    printf("\nRandom numbers:\n");
    for (int i = 0; i < 5; i++) {
        printf("%d ", rand() % 100); // Random number 0-99
    }
    printf("\n");
    
    // Absolute value
    int negative = -42;
    printf("Absolute value of %d = %d\n", negative, abs(negative));
    
    return 0;
}

Character Classification Functions (ctype.h)

Character Testing Functions

#include <stdio.h>
#include <ctype.h>

int main() {
    char test_chars[] = {'A', 'z', '5', '$', ' ', '\n'};
    int size = sizeof(test_chars) / sizeof(test_chars[0]);
    
    printf("Character Analysis:\n");
    printf("Char\tAlpha\tDigit\tUpper\tLower\tSpace\tPunct\n");
    printf("----\t-----\t-----\t-----\t-----\t-----\t-----\n");
    
    for (int i = 0; i < size; i++) {
        char ch = test_chars[i];
        printf("'%c'\t%d\t%d\t%d\t%d\t%d\t%d\n",
               (ch == '\n') ? 'n' : ch,
               isalpha(ch),
               isdigit(ch),
               isupper(ch),
               islower(ch),
               isspace(ch),
               ispunct(ch));
    }
    
    return 0;
}

Character Conversion Functions

#include <stdio.h>
#include <ctype.h>

int main() {
    char sentence[] = "Hello World 123!";
    char converted[100];
    int i;
    
    printf("Original: %s\n", sentence);
    
    // Convert to uppercase
    for (i = 0; sentence[i] != '\0'; i++) {
        converted[i] = toupper(sentence[i]);
    }
    converted[i] = '\0';
    printf("Uppercase: %s\n", converted);
    
    // Convert to lowercase
    for (i = 0; sentence[i] != '\0'; i++) {
        converted[i] = tolower(sentence[i]);
    }
    converted[i] = '\0';
    printf("Lowercase: %s\n", converted);
    
    return 0;
}

Time Functions (time.h)

Basic Time Operations

#include <stdio.h>
#include <time.h>

int main() {
    time_t current_time;
    struct tm *time_info;
    char time_string[100];
    
    // Get current time
    time(&current_time);
    printf("Current timestamp: %ld\n", current_time);
    
    // Convert to readable format
    time_info = localtime(&current_time);
    printf("Current time: %s", asctime(time_info));
    
    // Custom formatted time
    strftime(time_string, sizeof(time_string), "%Y-%m-%d %H:%M:%S", time_info);
    printf("Formatted time: %s\n", time_string);
    
    // Individual components
    printf("Year: %d\n", time_info->tm_year + 1900);
    printf("Month: %d\n", time_info->tm_mon + 1);
    printf("Day: %d\n", time_info->tm_mday);
    printf("Hour: %d\n", time_info->tm_hour);
    printf("Minute: %d\n", time_info->tm_min);
    printf("Second: %d\n", time_info->tm_sec);
    
    return 0;
}

Practical Examples

Text Processing Program

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

void analyzeText(char text[]) {
    int length = strlen(text);
    int words = 0, vowels = 0, consonants = 0, digits = 0;
    
    printf("Text Analysis for: \"%s\"\n", text);
    printf("Length: %d characters\n", length);
    
    for (int i = 0; i < length; i++) {
        char ch = tolower(text[i]);
        
        if (isalpha(ch)) {
            if (ch == 'a' || ch == 'e' || ch == 'i' || ch == 'o' || ch == 'u') {
                vowels++;
            } else {
                consonants++;
            }
        } else if (isdigit(ch)) {
            digits++;
        } else if (isspace(ch)) {
            words++;
        }
    }
    
    words++; // Add 1 for the last word
    
    printf("Words: %d\n", words);
    printf("Vowels: %d\n", vowels);
    printf("Consonants: %d\n", consonants);
    printf("Digits: %d\n", digits);
}

int main() {
    char text[200];
    
    printf("Enter a sentence: ");
    fgets(text, sizeof(text), stdin);
    
    // Remove newline if present
    if (text[strlen(text) - 1] == '\n') {
        text[strlen(text) - 1] = '\0';
    }
    
    analyzeText(text);
    
    return 0;
}

Calculator Program Using Built-in Functions

#include <stdio.h>
#include <math.h>
#include <stdlib.h>

void displayMenu() {
    printf("\n=== Scientific Calculator ===\n");
    printf("1. Basic Operations (+, -, *, /)\n");
    printf("2. Power and Square Root\n");
    printf("3. Trigonometric Functions\n");
    printf("4. Logarithmic Functions\n");
    printf("5. Exit\n");
    printf("Choose an option: ");
}

int main() {
    int choice;
    double num1, num2, result;
    
    while (1) {
        displayMenu();
        scanf("%d", &choice);
        
        switch (choice) {
            case 1:
                printf("Enter two numbers: ");
                scanf("%lf %lf", &num1, &num2);
                printf("%.2f + %.2f = %.2f\n", num1, num2, num1 + num2);
                printf("%.2f - %.2f = %.2f\n", num1, num2, num1 - num2);
                printf("%.2f * %.2f = %.2f\n", num1, num2, num1 * num2);
                if (num2 != 0) {
                    printf("%.2f / %.2f = %.2f\n", num1, num2, num1 / num2);
                } else {
                    printf("Division by zero error!\n");
                }
                break;
                
            case 2:
                printf("Enter number: ");
                scanf("%lf", &num1);
                printf("Square root of %.2f = %.2f\n", num1, sqrt(num1));
                printf("Enter base and exponent: ");
                scanf("%lf %lf", &num1, &num2);
                printf("%.2f ^ %.2f = %.2f\n", num1, num2, pow(num1, num2));
                break;
                
            case 3:
                printf("Enter angle in degrees: ");
                scanf("%lf", &num1);
                num1 = num1 * M_PI / 180.0; // Convert to radians
                printf("sin = %.4f\n", sin(num1));
                printf("cos = %.4f\n", cos(num1));
                printf("tan = %.4f\n", tan(num1));
                break;
                
            case 4:
                printf("Enter number: ");
                scanf("%lf", &num1);
                if (num1 > 0) {
                    printf("Natural log = %.4f\n", log(num1));
                    printf("Base-10 log = %.4f\n", log10(num1));
                } else {
                    printf("Logarithm undefined for non-positive numbers!\n");
                }
                break;
                
            case 5:
                printf("Thank you for using the calculator!\n");
                exit(0);
                
            default:
                printf("Invalid choice! Please try again.\n");
        }
    }
    
    return 0;
}

Common Built-in Functions Summary

Best Practices

1. Always include proper headers for the functions you use
2. Check return values for functions that can fail (like malloc)
3. Use appropriate data types for function parameters
4. Free allocated memory to prevent memory leaks
5. Validate input before passing to functions
6. Use const parameters when functions shouldn’t modify data

Summary

Built-in functions in C provide powerful, tested, and optimized solutions for common programming tasks. They save development time and reduce errors by providing standard implementations for I/O operations, string manipulation, mathematical calculations, memory management, and more. Understanding and effectively using these functions is essential for efficient C programming.

Part of BCA Programming with C Course (UGCOA22J201)