Write a program that prints the sum of its integer arguments on standard output and reports every failure through its exit status, not through a message on standard output.

• argv[1] to argv[argc - 1] are decimal integers. Print their sum followed by a newline, then return 0.
• A valid argument is an optional + or - sign followed by at least one digit, with nothing after the digits.
• Standard output carries the sum and nothing else. When the run fails it stays completely empty and the exit status carries the reason.
• Exit status 0: the sum is on standard output.
• Exit status 1: the program received no argument at all.
• Exit status 2: an argument is not a valid decimal integer, so an empty string, letters, a lone sign, or a leftover character such as 12x.
• Exit status 3: a value, or the sum being built, leaves the range of an int.
• Read the arguments left to right and stop on the first one that fails. The sum is checked at each step, so 2147483647 1 -1 is a 3 even though the final total would fit.
• Predict the overflow instead of observing it: compare against INT_MAX and INT_MIN before you add. Signed overflow has no defined behaviour in C, and a check written after the addition can be optimized away.
• You may only call write, so write your own string to integer conversion and your own number printing. atoi is out of reach on purpose: it returns 0 for "0" and for "gcc" alike, with no way to tell you which one it read.
• The wording of the diagnostic is yours. Send it to standard error, or send nothing: the grader reads standard output and the exit status only.

Write a program that prints the sum of its integer arguments on standard output and reports every failure through its exit status, not through a message on standard output.

• argv[1] to argv[argc - 1] are decimal integers. Print their sum followed by a newline, then return 0.
• A valid argument is an optional + or - sign followed by at least one digit, with nothing after the digits.
• Standard output carries the sum and nothing else. When the run fails it stays completely empty and the exit status carries the reason.
• Exit status 0: the sum is on standard output.
• Exit status 1: the program received no argument at all.
• Exit status 2: an argument is not a valid decimal integer, so an empty string, letters, a lone sign, or a leftover character such as 12x.
• Exit status 3: a value, or the sum being built, leaves the range of an int.
• Read the arguments left to right and stop on the first one that fails. The sum is checked at each step, so 2147483647 1 -1 is a 3 even though the final total would fit.
• Predict the overflow instead of observing it: compare against INT_MAX and INT_MIN before you add. Signed overflow has no defined behaviour in C, and a check written after the addition can be optimized away.
• You may only call write, so write your own string to integer conversion and your own number printing. atoi is out of reach on purpose: it returns 0 for "0" and for "gcc" alike, with no way to tell you which one it read.
• The wording of the diagnostic is yours. Send it to standard error, or send nothing: the grader reads standard output and the exit status only.