在此示例中，我不了解char的行为

Question

So I have the following code :

int main()
{
    int b=0;
    for(char c=0;c<256;c++)
        b++;
    cout<<b;
    return 0;
}

Why does it run indefinitely? (I tried c<255 - because I thought of char like a circle:once it reaches 360 degrees, it goes back from 0 and c<255 should break this loop - it turned out it still ran indefinitely)

Answer 1

Why does it run indefinitely?

Irrespective of whether char is signed type or unsigned type, it will not reach the value of 256 if char is represented by 8 bits, which is the most common representation. It will always be less than 256.

Answer 2

Why don't you run the code and print value to understand how char c in your code is getting incremented?

int b=0;
for(char c=0;c<256;c++)
{
    cout<<(int)c<<" ";
    b++;
    if(b == 256)break;
}

This code snippet outputs the following.

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29
30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56
57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83
84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 
108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 
-128 -127 -126 -125 -124 -123 -122 -121 -120 -119 -118 -117 -116 -115 -114 -113 
-112 -111 -110 -109 -108 -107 -106 -105 -104 -103 -102 -101 -100 -99 -98 -97 -96 
-95 -94 -93 -92 -91 -90 -89 -88 -87 -86 -85 -84 -83 -82 -81 -80 -79 -78 -77 -76 
-75 -74 -73 -72 -71 -70 -69 -68 -67 -66 -65 -64 -63 -62 -61 -60 -59 -58 -57 -56 
-55 -54 -53 -52 -51 -50 -49 -48 -47 -46 -45 -44 -43 -42 -41 -40 -39 -38 -37 -36 
-35 -34 -33 -32 -31 -30 -29 -28 -27 -26 -25 -24 -23 -22 -21 -20 -19 -18 -17 -16 
-15 -14 -13 -12 -11 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1

So, char never gets to 256. It gets to 127, and then when you try to increment it again, it wraps to -128.

Remember, typically char is represented by 8 bits and for signed char , the range is -128 to 127 and for unsigned char , the range is 0 to 255.

That's why, the condition c < 256 always evaluates to true and your code runs indefinitely.