DAY6 Embedded C Programming: Loops, Arrays, and goto

1. Loop Control

C provides multiple loop constructs for executing code repeatedly. Common loops include while, do...while, for, and unconditional loops using goto.

1.1 While Loop

int i = 0; // Initialization
while (i < 10) {
    printf("i = %d\n", i);
    i++; // Increment to eventually terminate the loop
}

• The condition expr1 is checked first; if true, the loop body executes.
• i++ gradually makes the condition false, ending the loop.
• Suitable for count-controlled loops.

1.2 Do…While Loop

int i = 0;
do {
    printf("i = %d\n", i);
    i++;
} while (i < 10);

• Executes the loop body before checking the condition.
• Ensures the loop body runs at least once.

1.3 Infinite Loop

while (1) {
    // Infinite loop body
}

• Commonly used in embedded systems for main loops or tasks.
• Make sure to include proper exit conditions or interrupts.

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2. Unconditional Jump with goto

goto allows unconditional jumps to a specified label, but it is not recommended in application-level code.

Example

int i = 0;

loop:
if (i < 10) {
    printf("i is %d\n", i);
    i++;
    goto loop;
}

• loop: defines the jump label.
• goto is often used in Linux kernel programming or for error handling.
• For general applications, prefer for or while loops instead.

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3. Nested Loops

Nested loops are commonly used in embedded systems for matrix operations or 2D array traversal, for example, printing a multiplication table:

for (int i = 1; i <= 9; i++) {
    for (int j = 1; j <= i; j++) {
        printf("%d*%d=%d ", i, j, i*j);
    }
    printf("\n");
}

• Outer loop runs once per iteration.
• Inner loop executes multiple times.
• Use continue to skip the current iteration or break to exit the loop.

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4. Loop Control Statements

• continue; → skips the rest of the current iteration, moving to the next.
• break; → immediately exits the loop.

Example

for (int i = 0; i < 5; i++) {
    for (int j = 0; j < 5; j++) {
        if (j == 3) continue; // Skip j=3
        if (i == 2) break;    // Exit inner loop when i=2
        printf("%d,%d\n", i, j);
    }
}

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5. Function Recursion

• Recursion is sometimes used in embedded programming.
• Be mindful of stack limitations, as deep recursion may cause stack overflow.

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6. Array Basics

An array is a finite collection of elements of the same type, widely used in embedded systems for data buffering and signal processing.

6.1 Defining Arrays

int a[5];      // Define an integer array of length 5
int b[2+4];    // Expressions can also be used for size

• Array elements are stored consecutively in memory.
• Indexing starts at 0, with the maximum index N-1.

6.2 Accessing Elements

a[0] = 10;   // First element
a[1] = 20;   // Second element
printf("%d\n", a[2]); // Third element

• Array indices can be variables, constants, or expressions.
• Arrays cannot be operated on as a whole, only individual elements.
• Avoid out-of-bounds access to prevent undefined behavior.

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