Programmer's---C language details 20 (symbolic and signed conversion, two number addition overflow after the numerical calculation)

Main content: Unsigned and signed conversions, two number addition overflow after the numerical calculation

#include <stdio.h>/* This function has a potential vulnerability */float sum_elements (float a[], unsigned length) {int i;float result = 0;for (i = 0; I <= length-1; i++) {result + = A[i];p rintf ("a[%d] =%f \ n", I,a[i]);} return result;}  int main () {int i = 200 * 300 * 400 * 500; int represents about 2 billion, unsigned on 4 billion float J = (3.14 + 1e20) -1e20;                       This statement outputs 3.14:float j = 3.14 + (1E20-1E20) because it represents a finite output result of 0.    e represents a low exponent of 10 long int a = 1;       A long long int b = 10;  printf ("i =%d\n", i);p rintf ("j =%f\n", j);p rintf ("a =%ld\n", a);p rintf ("b =%ld\n", b);p rintf ("\ n");/* Test complement */  unsigned int u = 4294967295u;int tu = (int) u;printf ("U =%u, tu =%d\n", u, tu); The maximum value of unsigned int is the same as the complement of-1 (that is, unsigned umax and-1 of the complement of the same bit) printf ("\ n");//If a signed number is mapped to its corresponding unsigned number, negative numbers are converted to large positive numbers, non-negative numbers remain unchanged/* Test converted */short int  v = -12345;unsigned Short UV = (unsigned short) v; The cast changes the value. But do not change the bit representation (i.e. 12345 and unsigned 53,191 bits as) printf ("V =%d, UV =%u\n", V, UV);  printf ("\ n"); float c[3];sum_elements (c,3); Error passing 0 o'clock with unsigned and signed conversion problems/* Summary: A number in the expression is signed and there is an unsigned, C languageThe default conversion to unsigned. There will be problems when comparing -1<0u *//* overflow calculation, the formula see */short a1 = -65536;short B1 = -1;printf ("\ n");p rintf ("%d\n", A1+B1); return 0;}

Overflow formula:

Output:

Programmer's---C language details 20 (symbolic and signed conversion, two number addition overflow after the numerical calculation)