L9: Multidimensional Arrays, String Library and Functions #

What are Multidimensional Arrays? #

In C, arrays can have two or more dimensions.
Commonly used: 2D arrays (like a matrix or table).
General form:

data_type array_name[size1][size2]...[sizeN];

Example:

int matrix[3][4]; // 3 rows, 4 columns

Memory Layout #

Stored in row-major order in C

Example:

int arr[2][3] = {
    {1, 2, 3},
    {4, 5, 6}
};

Stored as: 1, 2, 3, 4, 5, 6 in contiguous memory.

Example 1: Initializing and Printing #

#include <stdio.h>
int main() {
    int a[2][3] = {{1,2,3}, {4,5,6}};
    for(int i=0; i<2; i++) {
        for(int j=0; j<3; j++) {
            printf("%d ", a[i][j]);
        }
        printf("\n");
    }
    return 0;
}

Example 2: Sum of Elements in 2D Array #

#include <stdio.h>
int main() {
    int a[2][2] = {{10, 20}, {30, 40}};
    int sum = 0;
    for(int i=0; i<2; i++) {
        for(int j=0; j<2; j++) {
            sum += a[i][j];
        }
    }
    printf("Sum = %d\n", sum);
    return 0;
}

Example 3: Matrix Addition #

#include <stdio.h>
int main() {
    int A[2][2] = {{1, 2}, {3, 4}};
    int B[2][2] = {{5, 6}, {7, 8}};
    int C[2][2];

    for(int i=0; i<2; i++) {
        for(int j=0; j<2; j++) {
            C[i][j] = A[i][j] + B[i][j];
            printf("%d ", C[i][j]);
        }
        printf("\n");
    }
    return 0;
}

Example 4: Matrix Multiplication (3x3) #

#include <stdio.h>
int main() {
    int A[3][3] = {{1,2,3}, {4,5,6}, {7,8,9}};
    int B[3][3] = {{9,8,7}, {6,5,4}, {3,2,1}};
    int C[3][3] = {0};

    for(int i=0; i<3; i++) {
        for(int j=0; j<3; j++) {
            for(int k=0; k<3; k++) {
                C[i][j] += A[i][k] * B[k][j];
            }
            printf("%d ", C[i][j]);
        }
        printf("\n");
    }
    return 0;
}

Example 5: 3D Array #

#include <stdio.h>
int main() {
    int arr[2][2][2] = {
        { {1,2}, {3,4} },
        { {5,6}, {7,8} }
    };
    for(int i=0; i<2; i++) {
        for(int j=0; j<2; j++) {
            for(int k=0; k<2; k++) {
                printf("%d ", arr[i][j][k]);
            }
            printf("\n");
        }
        printf("\n");
    }
    return 0;
}

Strings in C: `<string.h>` #

Introduction #

Strings in C are arrays of char ending with '\0' (null terminator).
Standard library <string.h> provides functions for:
- Copying
- Concatenation
- Comparison
- Length calculation
- Searching

strlen – Find String Length #

#include <stdio.h>
#include <string.h>
int main() {
    char str[] = "Hello World";
    printf("Length = %lu\n", strlen(str));
    return 0;
}

strcpy & strncpy – Copy Strings #

#include <stdio.h>
#include <string.h>
int main() {
    char src[] = "C Programming";
    char dest[20];
    strcpy(dest, src);   // copy whole string
    printf("Copied: %s\n", dest);

    char dest2[10];
    strncpy(dest2, src, 5); // copy first 5 chars
    dest2[5] = '\0';        // add null terminator
    printf("Partial: %s\n", dest2);
    return 0;
}

strcat & strncat – Concatenate Strings #

#include <stdio.h>
#include <string.h>
int main() {
    char str1[30] = "Hello";
    char str2[] = " World";
    strcat(str1, str2);
    printf("%s\n", str1);

    char str3[30] = "Hello";
    strncat(str3, str2, 3); // Append first 3 chars
    printf("%s\n", str3);
    return 0;
}

strcmp – Compare Strings #

#include <stdio.h>
#include <string.h>
int main() {
    char a[] = "apple", b[] = "banana";
    int res = strcmp(a, b);
    if(res == 0)
        printf("Equal\n");
    else if(res < 0)
        printf("%s comes before %s\n", a, b);
    else
        printf("%s comes after %s\n", a, b);
    return 0;
}

Functions in C #

What are Functions? #

A function is a block of code that performs a specific task.
Helps in:
- Code reuse
- Better readability
- Modular programming
Types:
- Library functions (e.g., printf, scanf, sqrt)
- User-defined functions

Function Syntax #

return_type function_name(parameter_list) {
    // body of function
    return value; // if return_type is not void
}

return_type: type of value returned

function_name: identifier

parameter_list: input arguments (optional)

Example 1: Simple Function #

#include <stdio.h>

void greet() {
    printf("Hello, welcome to C programming!\n");
}

int main() {
    greet();   // function call
    return 0;
}

Example 2: Function with Parameters #

#include <stdio.h>

void printSum(int a, int b) {
    printf("Sum = %d\n", a + b);
}

int main() {
    printSum(5, 7);
    return 0;
}

Example 3: Function with Return Value #

#include <stdio.h>

int square(int x) {
    return x * x;
}

int main() {
    int result = square(6);
    printf("Square = %d\n", result);
    return 0;
}

Example 4: Multiple Functions #

#include <stdio.h>

int add(int a, int b) {
    return a + b;
}
int multiply(int a, int b) {
    return a * b;
}

int main() {
    printf("Add = %d\n", add(3,4));
    printf("Multiply = %d\n", multiply(3,4));
    return 0;
}

Function Declaration & Definition #

Declaration (prototype): tells compiler about function int add(int, int);

Definition: actual code body

int add(int a, int b) { return a + b; }

Call: using function name with arguments

int sum = add(5, 6);

Example 5: Recursive Function #

#include <stdio.h>

int factorial(int n) {
    if(n == 0) return 1;
    return n * factorial(n - 1);
}

int main() {
    printf("Factorial of 5 = %d\n", factorial(5));
    return 0;
}

Key Takeaways #

Functions improve modularity and code reuse.

Components:

Declaration (prototype)

Definition (body)

Call (usage)

Can have:

No parameters / no return

Parameters only

Return only

Both parameters and return

Recursion is when a function calls itself.