Week 10: Functions & Advanced C Concepts

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Q1. Call by Value

Concept: In call by value, the function receives a copy of the variable. Changes inside the function do not affect the original variable.

Program:

#include <stdio.h>

void change(int num); // Function prototype

int main() {    
    int x = 100;
    printf("Before function call x = %d\n", x);    
    change(x);    
    printf("After function call x = %d\n", x);    
    return 0;
}

void change(int num) {    
    printf("Before adding inside function num = %d\n", num);    
    num += 100;    
    printf("After adding inside function num = %d\n", num);    
}

Output Example:

Before function call x = 100
Before adding inside function num = 100
After adding inside function num = 200
After function call x = 100

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Q2. Call by Reference

Concept: In call by reference, the function receives the address of the variable, so changes inside the function modify the original variable.

Program:

#include <stdio.h>

void change(int *num); // Function prototype

int main() {    
    int x = 100;
    printf("Before function call x = %d\n", x);    
    change(&x);    
    printf("After function call x = %d\n", x);    
    return 0;
}

void change(int *num) {    
    printf("Before adding inside function num = %d\n", *num);    
    *num += 100;    
    printf("After adding inside function num = %d\n", *num);    
}

Output Example:

Before function call x = 100
Before adding inside function num = 100
After adding inside function num = 200
After function call x = 200

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Q3. Sum of Elements in an Array Using Function

Program:

#include <stdio.h>

float calculateSum(float num[], int size) {
    float sum = 0.0;
    for(int i = 0; i < size; i++)
        sum += num[i];
    return sum;
}

int main() {
    int size;
    printf("Enter number of elements: ");
    scanf("%d", &size);

    float num[size];
    printf("Enter elements: ");
    for(int i = 0; i < size; i++)
        scanf("%f", &num[i]);

    float result = calculateSum(num, size);
    printf("Sum = %.2f\n", result);
    return 0;
}

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Q4. Sort Array Using Selection Sort Function

Program:

#include <stdio.h>

void sort(int a[], int len) {
    for(int i = 0; i < len - 1; i++) {
        int min_index = i;
        for(int j = i + 1; j < len; j++) {
            if(a[j] < a[min_index])
                min_index = j;
        }
        int temp = a[i];
        a[i] = a[min_index];
        a[min_index] = temp;
    }
}

int main() {
    int len;
    printf("Enter number of elements: ");
    scanf("%d", &len);

    int a[len];
    printf("Enter elements: ");
    for(int i = 0; i < len; i++)
        scanf("%d", &a[i]);

    sort(a, len);

    printf("Sorted array: ");
    for(int i = 0; i < len; i++)
        printf("%d ", a[i]);
    printf("\n");

    return 0;
}

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Q5. Check Palindrome String Using Function

Program:

#include <stdio.h>

void palindrome(char str[]) {
    int left = 0, right = 0, flag = 1;

    // Find string length
    while(str[right] != '\0') right++;

    right--; // Last index

    // Check characters from both ends
    while(left < right) {
        if(str[left] != str[right]) {
            flag = 0;
            break;
        }
        left++;
        right--;
    }

    if(flag)
        printf("%s is a palindrome\n", str);
    else
        printf("%s is not a palindrome\n", str);
}

int main() {
    char str[100];
    printf("Enter a string: ");
    scanf("%s", str);

    palindrome(str);
    return 0;
}

Example:

Input: radar
Output: radar is a palindrome

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Key Points:

1. Call by Value: Only copies variable; original value unchanged.
2. Call by Reference: Pass address; function modifies original value.
3. Array Handling: Arrays are passed by reference by default in C.
4. Sorting: Selection sort repeatedly finds the minimum and swaps.
5. Palindrome Check: Compare characters from start and end until the middle.

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