C/C++ Tricky Programs

Here are 10 tricky C programming challenges that will test your understanding of language fundamentals and creative problem-solving techniques.

1. Program to Print Double Quotes in C

Printing double quotes in C requires escape sequences since quotes are used to delimit string literals. We use the backslash escape sequence " to print quotes −

#include <stdio.h>

int main() {
    printf(""Tutorials Point "");
    return 0;
}

"Tutorials Point "

2. Print Numbers 1 to 10 Without Loops or Goto

When loops and goto statements are forbidden, recursion provides an elegant solution for iteration −

#include <stdio.h>

void printNumber(int count) {
    printf("%d\n", count);
    count += 1;
    if (count <= 10)
        printNumber(count);
}

int main() {
    printNumber(1);
    return 0;
}

1
2
3
4
5
6
7
8
9
10

3. Check Equality Without Arithmetic or Comparison Operators

The XOR bitwise operator provides a clever way to check equality. If two numbers are equal, their XOR result is 0 −

#include <stdio.h>

int main() {
    int a = 132;
    int b = 132;
    
    if (a ^ b)
        printf("a is not equal to b");
    else
        printf("a is equal to b");
        
    return 0;
}

a is equal to b

4. Print "Hello" Without Using Semicolon

The printf() function returns the number of characters printed. We can exploit this return value in conditional statements −

#include <stdio.h>

int main() {
    if (printf("Hello "))
    return 0;
}

Hello 

5. Find Maximum and Minimum Without Comparison Operators

Using the absolute value function abs(), we can determine max and min through mathematical manipulation −

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

int main() {
    int x = 15, y = 20;
    printf("The numbers are x = %d and y = %d\n", x, y);
    printf("The max of the numbers is %d\n", ((x + y) + abs(x - y)) / 2);
    printf("The min of the numbers is %d\n", ((x + y) - abs(x - y)) / 2);
    return 0;
}

The numbers are x = 15 and y = 20
The max of the numbers is 20
The min of the numbers is 15

6. Print Source Code of the Program

This self-referencing program uses the __FILE__ macro to open and print its own source code −

#include <stdio.h>

int main(void) {
    FILE *program;
    char ch;
    program = fopen(__FILE__, "r");
    
    if (program == NULL) {
        printf("Error opening file");
        return 1;
    }
    
    do {
        ch = fgetc(program);
        printf("%c", ch);
    } while (ch != EOF);
    
    fclose(program);
    return 0;
}

7. Sum Two Numbers Without Plus Operator

Mathematical manipulation using subtraction and negation can achieve addition −

#include <stdio.h>

int main() {
    int x = 5;
    int y = 5;
    int sum = x - (-y);
    
    printf("The numbers are x = %d y = %d\n", x, y);
    printf("Their sum = %d", sum);
    return 0;
}

The numbers are x = 5 y = 5
Their sum = 10

8. Check Even Number Without Arithmetic or Relational Operators

Bitwise AND with 1 checks the least significant bit. If it's 1, the number is odd; if 0, it's even −

#include <stdio.h>

int main() {
    int a = 154;
    
    if (a & 1) {
        printf("%d is an odd number", a);
    } else {
        printf("%d is an even number", a);
    }
    
    return 0;
}

154 is an even number

9. Divide by 4 Without Division Operator

Right shift by 2 positions effectively divides by 4 (since 4 = 2²) −

#include <stdio.h>

int main() {
    int n = 128;
    printf("%d divided by 4 = ", n);
    n = n >> 2;
    printf("%d", n);
    return 0;
}

128 divided by 4 = 32

10. Recursive Sum of Digits Until Single Digit

This uses a mathematical property: the recursive sum of digits equals (n-1) % 9 + 1 for positive numbers −

#include <stdio.h>

int main() {
    int a = 534;
    int sum;
    
    if (a)
        sum = a % 9 == 0 ? 9 : a % 9;
    else
        sum = 0;
        
    printf("The final sum is %d", sum);
    return 0;
}

The final sum is 3

Conclusion

These tricky programs demonstrate creative problem-solving in C using bitwise operations, recursion, mathematical properties, and language-specific features. They showcase how constraints can lead to innovative programming solutions.