1+2+3+....+n(循环)
#includemain() { int a = 1, sum = 0, n; printf("Input n:"); scanf("%d", &n); do { sum += a; a++; } while (a <= n); printf("sum = %dn", sum); }

1+2+3+....+n(循环)
#includemain() { int a = 1, sum = 0, n; printf("Input n:"); scanf("%d", &n); do { sum += a; a++; } while (a <= n); printf("sum = %dn", sum); }