Register keyword in C

 The "register" keyword in C is used to suggest to the compiler that a variable should be stored in a CPU register for faster access.

 However, its usage and effectiveness have diminished over time due to modern compiler optimizations.

syntax of using the register keyword:

register int variable_name;

 When you declare a variable with the register keyword, you're suggesting to the compiler that frequent accesses to this variable should be optimized by storing it in a CPU register, which is faster than accessing memory.

 However, it's important to note that the compiler is not obligated to comply with this suggestion; it may choose to ignore it based on various factors like optimization level, variable size, and the number of available registers.

Example:

// Program for register in C
#include<stdio.h> 

int main() {
    register int T; // Declare T as a register variable
    int sum = 0;

    for (T = 1; T <= 1000; ++T) {
        sum += T; // Accumulate sum
    }

    printf("Sum: %d\n", sum);

    return 0;
}

Output:

Sum: 500500

In this program, the variable T is declared as a register variable.

The compiler is encouraged to store it in a register for faster access within the loop.

However, the effectiveness of this optimization depends on various factors, and modern compilers often perform register allocation and optimization automatically, making the explicit use of the register keyword less impactful.