Register Storage Class
The register variable is stored in the computer CPU register, since register access is faster than the memory access. If the CPU fails to keep the variables in CPU registers, in that case the variables are assumed as auto and stored in the memory because CPU registers are limited in numbers. Hence the compiler automatically converts register variables to non register variables once the limit is reached. When you declare float and double variable as register, it treats as auto variable because it takes more space to store.
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S.No.
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Features of External Variable
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Meaning
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1.
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Storage or location of variable
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CPU Register
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2.
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Initial or default value
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Garbage Value or Unpredictable value
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3.
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Scope of the variable
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Local to the block in which the variable is defined
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4.
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Life of the variable
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Till the control remains within the block in which the variable is defined.
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Example of Register storage class
main()
{
register int num;
for(num=1;num<=5;num++)
printf("\t%d",num);
}
Output: 1 2 3 4 5
Explanation: The variable num is stored in CPU register till the loop executed successfully.