Control Flow & Decision Making

1#include <stdio.h>
2
3int main() {
4    // Demonstrating true/false values
5    printf("=== True/False in C ===\n\n");
6    
7    // Zero is FALSE
8    if (0) {
9        printf("0: This won't print\n");
10    } else {
11        printf("0: FALSE (block skipped)\n");
12    }
13    
14    // Non-zero is TRUE
15    if (1) printf("1: TRUE\n");
16    if (-5) printf("-5: TRUE (negative numbers are non-zero)\n");
17    if (100) printf("100: TRUE\n");
18    
19    // Comparison results
20    printf("\n=== Comparisons Return 0 or 1 ===\n");
21    printf("5 > 3  = %d (TRUE)\n", 5 > 3);
22    printf("5 < 3  = %d (FALSE)\n", 5 < 3);
23    printf("5 == 5 = %d (TRUE)\n", 5 == 5);
24    printf("5 != 5 = %d (FALSE)\n", 5 != 5);
25    
26    // You can store comparison results
27    int isAdult = (25 >= 18);  // isAdult = 1
28    printf("\n25 >= 18 stored in variable: %d\n", isAdult);
29    
30    return 0;
31}

1#include <stdio.h>
2
3int main() {
4    int temperature = 35;
5    
6    printf("Temperature: %d°C\n", temperature);
7    
8    // Simple if statement
9    if (temperature > 30) {
10        printf("It's hot today!\n");
11        printf("Consider staying hydrated.\n");
12    }
13    
14    printf("Weather check complete.\n");
15    
16    return 0;
17}

1#include <stdio.h>
2
3int main() {
4    int number = 17;
5    
6    printf("Number: %d\n", number);
7    
8    // Even numbers have remainder 0 when divided by 2
9    if (number % 2 == 0) {
10        printf("%d is EVEN\n", number);
11    }
12    else {
13        printf("%d is ODD\n", number);
14    }
15    
16    return 0;
17}

1#include <stdio.h>
2
3int main() {
4    int marks = 73;
5    char grade;
6    
7    printf("Marks: %d\n", marks);
8    
9    if (marks >= 90) {
10        grade = 'A';
11        printf("Excellent work!\n");
12    }
13    else if (marks >= 80) {
14        grade = 'B';
15        printf("Great job!\n");
16    }
17    else if (marks >= 70) {
18        grade = 'C';
19        printf("Good effort!\n");
20    }
21    else if (marks >= 60) {
22        grade = 'D';
23        printf("You passed.\n");
24    }
25    else {
26        grade = 'F';
27        printf("Need improvement.\n");
28    }
29    
30    printf("Grade: %c\n", grade);
31    
32    return 0;
33}

1#include <stdio.h>
2
3int main() {
4    int age = 20;
5    int isCitizen = 1;  // 1 = true, 0 = false
6    
7    printf("Age: %d, Citizen: %s\n", age, isCitizen ? "Yes" : "No");
8    
9    if (isCitizen) {
10        // Only check age if they're a citizen
11        if (age >= 18) {
12            printf("✓ You can vote!\n");
13        }
14        else {
15            printf("✗ Too young to vote (must be 18+).\n");
16        }
17    }
18    else {
19        printf("✗ Only citizens can vote.\n");
20    }
21    
22    return 0;
23}

1#include <stdio.h>
2
3int main() {
4    int day = 3;
5    
6    printf("Day number: %d\n", day);
7    printf("Day name: ");
8    
9    switch (day) {
10        case 1:
11            printf("Monday\n");
12            break;
13        case 2:
14            printf("Tuesday\n");
15            break;
16        case 3:
17            printf("Wednesday\n");
18            break;
19        case 4:
20            printf("Thursday\n");
21            break;
22        case 5:
23            printf("Friday\n");
24            break;
25        case 6:
26            printf("Saturday\n");
27            break;
28        case 7:
29            printf("Sunday\n");
30            break;
31        default:
32            printf("Invalid day (use 1-7)\n");
33    }
34    
35    return 0;
36}

1#include <stdio.h>
2
3int main() {
4    int day = 6;
5    
6    printf("Day %d is a ", day);
7    
8    switch (day) {
9        case 1:
10        case 2:
11        case 3:
12        case 4:
13        case 5:
14            printf("Weekday\n");
15            break;
16        case 6:
17        case 7:
18            printf("Weekend!\n");
19            break;
20        default:
21            printf("Invalid day\n");
22    }
23    
24    return 0;
25}

1#include <stdio.h>
2
3int main() {
4    int numbers[] = {10, 25, 33, 47, 56, 68, 72};
5    int size = 7;
6    int target = 47;
7    int found = 0;
8    
9    printf("Searching for %d...\n", target);
10    
11    for (int i = 0; i < size; i++) {
12        printf("Checking index %d: %d\n", i, numbers[i]);
13        
14        if (numbers[i] == target) {
15            printf(">>> Found %d at index %d!\n", target, i);
16            found = 1;
17            break;  // Exit loop immediately - no need to check rest
18        }
19    }
20    
21    if (!found) {
22        printf("Value not found.\n");
23    }
24    
25    printf("Search complete.\n");
26    return 0;
27}

1#include <stdio.h>
2
3int main() {
4    int numbers[] = {5, -3, 10, -7, 8, -2, 15};
5    int size = 7;
6    int sum = 0;
7    
8    printf("Processing numbers (skipping negatives):\n");
9    
10    for (int i = 0; i < size; i++) {
11        // Skip negative numbers
12        if (numbers[i] < 0) {
13            printf("Skipping %d (negative)\n", numbers[i]);
14            continue;  // Jump to next iteration
15        }
16        
17        // This code only runs for positive numbers
18        printf("Adding %d\n", numbers[i]);
19        sum += numbers[i];
20    }
21    
22    printf("\nSum of positive numbers: %d\n", sum);
23    return 0;
24}

1#include <stdio.h>
2
3int main() {
4    int grid[3][3] = {
5        {1, 2, 3},
6        {4, 5, 6},
7        {7, 8, 9}
8    };
9    int target = 5;
10    int found_row = -1, found_col = -1;
11    
12    printf("Searching for %d in 3x3 grid...\n\n", target);
13    
14    // Nested loops - break would only exit inner loop
15    for (int i = 0; i < 3; i++) {
16        for (int j = 0; j < 3; j++) {
17            printf("Checking [%d][%d] = %d\n", i, j, grid[i][j]);
18            
19            if (grid[i][j] == target) {
20                found_row = i;
21                found_col = j;
22                goto found;  // Exit BOTH loops at once
23            }
24        }
25    }
26    
27    // Only reaches here if not found
28    printf("\nValue not found in grid.\n");
29    goto end;
30    
31found:
32    printf("\n>>> Found %d at position [%d][%d]!\n", target, found_row, found_col);
33    
34end:
35    printf("Search complete.\n");
36    return 0;
37}

1#include <stdio.h>
2#include <stdlib.h>
3
4int main() {
5    FILE *file = NULL;
6    char *buffer = NULL;
7    int result = 0;
8    
9    // Allocate memory
10    buffer = malloc(100);
11    if (buffer == NULL) {
12        printf("Error: Memory allocation failed\n");
13        goto cleanup;  // Jump to cleanup
14    }
15    
16    // Open file
17    file = fopen("data.txt", "r");
18    if (file == NULL) {
19        printf("Error: Cannot open file\n");
20        goto cleanup;  // Jump to cleanup
21    }
22    
23    // Process file...
24    printf("Processing file...\n");
25    result = 1;  // Success
26    
27cleanup:  // Single cleanup point for all exits
28    if (file != NULL) {
29        fclose(file);
30        printf("File closed.\n");
31    }
32    if (buffer != NULL) {
33        free(buffer);
34        printf("Memory freed.\n");
35    }
36    
37    return result ? 0 : 1;
38}